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6502 Microprocessor
Most of the following information has been taking out of the "Commodore 64
Programmers Reference Manual" simply because it was available in electronic
form and there appears to be no difference between this documentation and
the 6502 documentation, they are both from the 6500 family after all. I've
made changes and additions where appropriate.
In theory you should be able to use any code you can find for emulating
the 6510 (the C64 processor).
THE REGISTERS INSIDE THE 6502 MICROPROCESSOR
Almost all calculations are done in the microprocessor. Registers are
special pieces of memory in the processor which are used to carry out, and
store information about calculations. The 6502 has the following registers:
THE ACCUMULATOR
This is THE most important register in the microprocessor. Various ma-
chine language instructions allow you to copy the contents of a memory
location into the accumulator, copy the contents of the accumulator into
a memory location, modify the contents of the accumulator or some other
register directly, without affecting any memory. And the accumulator is
the only register that has instructions for performing math.
THE X INDEX REGISTER
This is a very important register. There are instructions for nearly
all of the transformations you can make to the accumulator. But there are
other instructions for things that only the X register can do. Various
machine language instructions allow you to copy the contents of a memory
location into the X register, copy the contents of the X register into a
memory location, and modify the contents of the X, or some other register
directly.
THE Y INDEX REGISTER
This is a very important register. There are instructions for nearly
all of the transformations you can make to the accumulator, and the X
register. But there are other instructions for things that only the Y
register can do. Various machine language instructions allow you to copy
the contents of a memory location into the Y register, copy the contents
of the Y register into a memory location, and modify the contents of the
Y, or some other register directly.
THE STATUS REGISTER
This register consists of eight "flags" (a flag = something that indi-
cates whether something has, or has not occurred). Bits of this register
are altered depending on the result of arithmetic and logical operations.
These bits are described below:
Bit No. 7 6 5 4 3 2 1 0
S V B D I Z C
Bit0 - C - Carry flag: this holds the carry out of the most significant
bit in any arithmetic operation. In subtraction operations however, this
flag is cleared - set to 0 - if a borrow is required, set to 1 - if no
borrow is required. The carry flag is also used in shift and rotate
logical operations.
Bit1 - Z - Zero flag: this is set to 1 when any arithmetic or logical
operation produces a zero result, and is set to 0 if the result is
non-zero.
Bit 2 - I: this is an interrupt enable/disable flag. If it is set,
interrupts are disabled. If it is cleared, interrupts are enabled.
Bit 3 - D: this is the decimal mode status flag. When set, and an Add with
Carry or Subtract with Carry instruction is executed, the source values are
treated as valid BCD (Binary Coded Decimal, eg. 0x00-0x99 = 0-99) numbers.
The result generated is also a BCD number.
Bit 4 - B: this is set when a software interrupt (BRK instruction) is
executed.
Bit 5: not used. Supposed to be logical 1 at all times.
Bit 6 - V - Overflow flag: when an arithmetic operation produces a result
too large to be represented in a byte, V is set.
Bit 7 - S - Sign flag: this is set if the result of an operation is
negative, cleared if positive.
The most commonly used flags are C, Z, V, S.
THE PROGRAM COUNTER
This contains the address of the current machine language instruction
being executed. Since the operating system is always "RUN"ning in the
Commodore VIC-20 (or, for that matter, any computer), the program counter
is always changing. It could only be stopped by halting the microprocessor
in some way.
THE STACK POINTER
This register contains the location of the first empty place on the
stack. The stack is used for temporary storage by machine language pro-
grams, and by the computer.
ADDRESSING MODES
Instructions need operands to work on. There are various ways of
indicating where the processor is to get these operands. The different
methods used to do this are called addressing modes. The 6502 offers 11
modes, as described below.
1) Immediate
In this mode the operand's value is given in the instruction itself. In
assembly language this is indicated by "#" before the operand.
eg. LDA #$0A - means "load the accumulator with the hex value 0A"
In machine code different modes are indicated by different codes. So LDA
would be translated into different codes depending on the addressing mode.
In this mode, it is: $A9 $0A
2 & 3) Absolute and Zero-page Absolute
In these modes the operands address is given.
eg. LDA $31F6 - (assembler)
$AD $31F6 - (machine code)
If the address is on zero page - i.e. any address where the high byte is
00 - only 1 byte is needed for the address. The processor automatically
fills the 00 high byte.
eg. LDA $F4
$A5 $F4
Note the different instruction codes for the different modes.
Note also that for 2 byte addresses, the low byte is store first, eg.
LDA $31F6 is stored as three bytes in memory, $AD $F6 $31.
Zero-page absolute is usually just called zero-page.
4) Implied
No operand addresses are required for this mode. They are implied by the
instruction.
eg. TAX - (transfer accumulator contents to X-register)
$AA
5) Accumulator
In this mode the instruction operates on data in the accumulator, so no
operands are needed.
eg. LSR - logical bit shift right
$4A
6 & 7) Indexed and Zero-page Indexed
In these modes the address given is added to the value in either the X or
Y index register to give the actual address of the operand.
eg. LDA $31F6, Y
$D9 $31F6
LDA $31F6, X
$DD $31F6
Note that the different operation codes determine the index register used.
In the zero-page version, you should note that the X and Y registers are
not interchangeable. Most instructions which can be used with zero-page
indexing do so with X only.
eg. LDA $20, X
$B5 $20
8) Indirect
This mode applies only to the JMP instruction - JuMP to new location. It is
indicated by parenthesis around the operand. The operand is the address of
the bytes whose value is the new location.
eg. JMP ($215F)
Assume the following - byte value
$215F $76
$2160 $30
This instruction takes the value of bytes $215F, $2160 and uses that as the
address to jump to - i.e. $3076 (remember that addresses are stored with
low byte first).
9) Pre-indexed indirect
In this mode a zer0-page address is added to the contents of the X-register
to give the address of the bytes holding the address of the operand. The
indirection is indicated by parenthesis in assembly language.
eg. LDA ($3E, X)
$A1 $3E
Assume the following - byte value
X-reg. $05
$0043 $15
$0044 $24
$2415 $6E
Then the instruction is executed by:
(i) adding $3E and $05 = $0043
(ii) getting address contained in bytes $0043, $0044 = $2415
(iii) loading contents of $2415 - i.e. $6E - into accumulator
Note a) When adding the 1-byte address and the X-register, wrap around
addition is used - i.e. the sum is always a zero-page address.
eg. FF + 2 = 0001 not 0101 as you might expect.
DON'T FORGET THIS WHEN EMULATING THIS MODE.
b) Only the X register is used in this mode.
10) Post-indexed indirect
In this mode the contents of a zero-page address (and the following byte)
give the indirect addressm which is added to the contents of the Y-register
to yield the actual address of the operand. Again, inassembly language,
the instruction is indicated by parenthesis.
eg. LDA ($4C), Y
Note that the parenthesis are only around the 2nd byte of the instruction
since it is the part that does the indirection.
Assume the following - byte value
$004C $00
$004D $21
Y-reg. $05
$2105 $6D
Then the instruction above executes by:
(i) getting the address in bytes $4C, $4D = $2100
(ii) adding the contents of the Y-register = $2105
(111) loading the contents of the byte $2105 - i.e. $6D into the
accumulator.
Note: only the Y-register is used in this mode.
11) Relative
This mode is used with Branch-on-Condition instructions. It is probably
the mode you will use most often. A 1 byte value is added to the program
counter, and the program continues execution from that address. The 1
byte number is treated as a signed number - i.e. if bit 7 is 1, the number
given byt bits 0-6 is negative; if bit 7 is 0, the number is positive. This
enables a branch displacement of up to 127 bytes in either direction.
eg bit no. 7 6 5 4 3 2 1 0 signed value unsigned value
value 1 0 1 0 0 1 1 1 -39 $A7
value 0 0 1 0 0 1 1 1 +39 $27
Instruction example:
BEQ $A7
$F0 $A7
This instruction will check the zero status bit. If it is set, 39 decimal
will be subtracted from the program counter and execution continues from
that address. If the zero status bit is not set, execution continues from
the following instruction.
Notes: a) The program counter points to the start of the instruction
after the branch instruction before the branch displacement is added.
Remember to take this into account when calculating displacements.
b) Branch-on-condition instructions work by checking the relevant
status bits in the status register. Make sure that they have been set or
unset as you want them. This is often done using a CMP instruction.
c) If you find you need to branch further than 127 bytes, use the
opposite branch-on-condition and a JMP.
+------------------------------------------------------------------------
|
| MCS6502 MICROPROCESSOR INSTRUCTION SET - ALPHABETIC SEQUENCE
|
+------------------------------------------------------------------------
|
| ADC Add Memory to Accumulator with Carry
| AND "AND" Memory with Accumulator
| ASL Shift Left One Bit (Memory or Accumulator)
|
| BCC Branch on Carry Clear
| BCS Branch on Carry Set
| BEQ Branch on Result Zero
| BIT Test Bits in Memory with Accumulator
| BMI Branch on Result Minus
| BNE Branch on Result not Zero
| BPL Branch on Result Plus
| BRK Force Break
| BVC Branch on Overflow Clear
| BVS Branch on Overflow Set
|
| CLC Clear Carry Flag
| CLD Clear Decimal Mode
| CLI Clear interrupt Disable Bit
| CLV Clear Overflow Flag
| CMP Compare Memory and Accumulator
| CPX Compare Memory and Index X
| CPY Compare Memory and Index Y
|
| DEC Decrement Memory by One
| DEX Decrement Index X by One
| DEY Decrement Index Y by One
|
| EOR "Exclusive-Or" Memory with Accumulator
|
| INC Increment Memory by One
| INX Increment Index X by One
| INY Increment Index Y by One
|
| JMP Jump to New Location
|
+------------------------------------------------------------------------
------------------------------------------------------------------------+
|
MCS6502 MICROPROCESSOR INSTRUCTION SET - ALPHABETIC SEQUENCE |
|
------------------------------------------------------------------------+
|
JSR Jump to New Location Saving Return Address |
|
LDA Load Accumulator with Memory |
LDX Load Index X with Memory |
LDY Load Index Y with Memory |
LSR Shift Right One Bit (Memory or Accumulator) |
|
NOP No Operation |
|
ORA "OR" Memory with Accumulator |
|
PHA Push Accumulator on Stack |
PHP Push Processor Status on Stack |
PLA Pull Accumulator from Stack |
PLP Pull Processor Status from Stack |
|
ROL Rotate One Bit Left (Memory or Accumulator) |
ROR Rotate One Bit Right (Memory or Accumulator) |
RTI Return from Interrupt |
RTS Return from Subroutine |
|
SBC Subtract Memory from Accumulator with Borrow |
SEC Set Carry Flag |
SED Set Decimal Mode |
SEI Set Interrupt Disable Status |
STA Store Accumulator in Memory |
STX Store Index X in Memory |
STY Store Index Y in Memory |
|
TAX Transfer Accumulator to Index X |
TAY Transfer Accumulator to Index Y |
TSX Transfer Stack Pointer to Index X |
TXA Transfer Index X to Accumulator |
TXS Transfer Index X to Stack Pointer |
TYA Transfer Index Y to Accumulator |
------------------------------------------------------------------------+
The following notation applies to this summary:
A Accumulator EOR Logical Exclusive Or
X, Y Index Registers fromS Transfer from Stack
M Memory toS Transfer to Stack
P Processor Status Register -> Transfer to
S Stack Pointer <- Transfer from
/ Change V Logical OR
_ No Change PC Program Counter
+ Add PCH Program Counter High
/\ Logical AND PCL Program Counter Low
- Subtract OPER OPERAND
# IMMEDIATE ADDRESSING MODE
Note: At the top of each table is located in parentheses a reference
number (Ref: XX) which directs the user to that Section in the
MCS6500 Microcomputer Family Programming Manual in which the
instruction is defined and discussed.
ADC Add memory to accumulator with carry ADC
Operation: A + M + C -> A, C N Z C I D V
/ / / _ _ /
(Ref: 2.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | ADC #Oper | 69 | 2 | 2 |
| Zero Page | ADC Oper | 65 | 2 | 3 |
| Zero Page,X | ADC Oper,X | 75 | 2 | 4 |
| Absolute | ADC Oper | 60 | 3 | 4 |
| Absolute,X | ADC Oper,X | 70 | 3 | 4* |
| Absolute,Y | ADC Oper,Y | 79 | 3 | 4* |
| (Indirect,X) | ADC (Oper,X) | 61 | 2 | 6 |
| (Indirect),Y | ADC (Oper),Y | 71 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
AND "AND" memory with accumulator AND
Operation: A /\ M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.0)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | AND #Oper | 29 | 2 | 2 |
| Zero Page | AND Oper | 25 | 2 | 3 |
| Zero Page,X | AND Oper,X | 35 | 2 | 4 |
| Absolute | AND Oper | 2D | 3 | 4 |
| Absolute,X | AND Oper,X | 3D | 3 | 4* |
| Absolute,Y | AND Oper,Y | 39 | 3 | 4* |
| (Indirect,X) | AND (Oper,X) | 21 | 2 | 6 |
| (Indirect,Y) | AND (Oper),Y | 31 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
ASL ASL Shift Left One Bit (Memory or Accumulator) ASL
+-+-+-+-+-+-+-+-+
Operation: C <- |7|6|5|4|3|2|1|0| <- 0
+-+-+-+-+-+-+-+-+ N Z C I D V
/ / / _ _ _
(Ref: 10.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ASL A | 0A | 1 | 2 |
| Zero Page | ASL Oper | 06 | 2 | 5 |
| Zero Page,X | ASL Oper,X | 16 | 2 | 6 |
| Absolute | ASL Oper | 0E | 3 | 6 |
| Absolute, X | ASL Oper,X | 1E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
BCC BCC Branch on Carry Clear BCC
N Z C I D V
Operation: Branch on C = 0 _ _ _ _ _ _
(Ref: 4.1.1.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BCC Oper | 90 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BCS BCS Branch on carry set BCS
Operation: Branch on C = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BCS Oper | B0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to next page.
BEQ BEQ Branch on result zero BEQ
N Z C I D V
Operation: Branch on Z = 1 _ _ _ _ _ _
(Ref: 4.1.1.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BEQ Oper | F0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to next page.
BIT BIT Test bits in memory with accumulator BIT
Operation: A /\ M, M7 -> N, M6 -> V
Bit 6 and 7 are transferred to the status register. N Z C I D V
If the result of A /\ M is zero then Z = 1, otherwise M7/ _ _ _ M6
Z = 0
(Ref: 4.2.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | BIT Oper | 24 | 2 | 3 |
| Absolute | BIT Oper | 2C | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
BMI BMI Branch on result minus BMI
Operation: Branch on N = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BMI Oper | 30 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 1 if branch occurs to different page.
BNE BNE Branch on result not zero BNE
Operation: Branch on Z = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BMI Oper | D0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BPL BPL Branch on result plus BPL
Operation: Branch on N = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BPL Oper | 10 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BRK BRK Force Break BRK
Operation: Forced Interrupt PC + 2 toS P toS N Z C I D V
_ _ _ 1 _ _
(Ref: 9.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | BRK | 00 | 1 | 7 |
+----------------+-----------------------+---------+---------+----------+
1. A BRK command cannot be masked by setting I.
BVC BVC Branch on overflow clear BVC
Operation: Branch on V = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BVC Oper | 50 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BVS BVS Branch on overflow set BVS
Operation: Branch on V = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BVS Oper | 70 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
CLC CLC Clear carry flag CLC
Operation: 0 -> C N Z C I D V
_ _ 0 _ _ _
(Ref: 3.0.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLC | 18 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CLD CLD Clear decimal mode CLD
Operation: 0 -> D N A C I D V
_ _ _ _ 0 _
(Ref: 3.3.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLD | D8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CLI CLI Clear interrupt disable bit CLI
Operation: 0 -> I N Z C I D V
_ _ _ 0 _ _
(Ref: 3.2.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLI | 58 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CLV CLV Clear overflow flag CLV
Operation: 0 -> V N Z C I D V
_ _ _ _ _ 0
(Ref: 3.6.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLV | B8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CMP CMP Compare memory and accumulator CMP
Operation: A - M N Z C I D V
/ / / _ _ _
(Ref: 4.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CMP #Oper | C9 | 2 | 2 |
| Zero Page | CMP Oper | C5 | 2 | 3 |
| Zero Page,X | CMP Oper,X | D5 | 2 | 4 |
| Absolute | CMP Oper | CD | 3 | 4 |
| Absolute,X | CMP Oper,X | DD | 3 | 4* |
| Absolute,Y | CMP Oper,Y | D9 | 3 | 4* |
| (Indirect,X) | CMP (Oper,X) | C1 | 2 | 6 |
| (Indirect),Y | CMP (Oper),Y | D1 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
CPX CPX Compare Memory and Index X CPX
N Z C I D V
Operation: X - M / / / _ _ _
(Ref: 7.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CPX *Oper | E0 | 2 | 2 |
| Zero Page | CPX Oper | E4 | 2 | 3 |
| Absolute | CPX Oper | EC | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
CPY CPY Compare memory and index Y CPY
N Z C I D V
Operation: Y - M / / / _ _ _
(Ref: 7.9)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CPY *Oper | C0 | 2 | 2 |
| Zero Page | CPY Oper | C4 | 2 | 3 |
| Absolute | CPY Oper | CC | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
DEC DEC Decrement memory by one DEC
Operation: M - 1 -> M N Z C I D V
/ / _ _ _ _
(Ref: 10.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | DEC Oper | C6 | 2 | 5 |
| Zero Page,X | DEC Oper,X | D6 | 2 | 6 |
| Absolute | DEC Oper | CE | 3 | 6 |
| Absolute,X | DEC Oper,X | DE | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
DEX DEX Decrement index X by one DEX
Operation: X - 1 -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | DEX | CA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
DEY DEY Decrement index Y by one DEY
Operation: X - 1 -> Y N Z C I D V
/ / _ _ _ _
(Ref: 7.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | DEY | 88 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
EOR EOR "Exclusive-Or" memory with accumulator EOR
Operation: A EOR M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | EOR #Oper | 49 | 2 | 2 |
| Zero Page | EOR Oper | 45 | 2 | 3 |
| Zero Page,X | EOR Oper,X | 55 | 2 | 4 |
| Absolute | EOR Oper | 40 | 3 | 4 |
| Absolute,X | EOR Oper,X | 50 | 3 | 4* |
| Absolute,Y | EOR Oper,Y | 59 | 3 | 4* |
| (Indirect,X) | EOR (Oper,X) | 41 | 2 | 6 |
| (Indirect),Y | EOR (Oper),Y | 51 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
INC INC Increment memory by one INC
N Z C I D V
Operation: M + 1 -> M / / _ _ _ _
(Ref: 10.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | INC Oper | E6 | 2 | 5 |
| Zero Page,X | INC Oper,X | F6 | 2 | 6 |
| Absolute | INC Oper | EE | 3 | 6 |
| Absolute,X | INC Oper,X | FE | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
INX INX Increment Index X by one INX
N Z C I D V
Operation: X + 1 -> X / / _ _ _ _
(Ref: 7.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | INX | E8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
INY INY Increment Index Y by one INY
Operation: X + 1 -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | INY | C8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
JMP JMP Jump to new location JMP
Operation: (PC + 1) -> PCL N Z C I D V
(PC + 2) -> PCH (Ref: 4.0.2) _ _ _ _ _ _
(Ref: 9.8.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Absolute | JMP Oper | 4C | 3 | 3 |
| Indirect | JMP (Oper) | 6C | 3 | 5 |
+----------------+-----------------------+---------+---------+----------+
JSR JSR Jump to new location saving return address JSR
Operation: PC + 2 toS, (PC + 1) -> PCL N Z C I D V
(PC + 2) -> PCH _ _ _ _ _ _
(Ref: 8.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Absolute | JSR Oper | 20 | 3 | 6 |
+----------------+-----------------------+---------+---------+----------+
LDA LDA Load accumulator with memory LDA
Operation: M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDA #Oper | A9 | 2 | 2 |
| Zero Page | LDA Oper | A5 | 2 | 3 |
| Zero Page,X | LDA Oper,X | B5 | 2 | 4 |
| Absolute | LDA Oper | AD | 3 | 4 |
| Absolute,X | LDA Oper,X | BD | 3 | 4* |
| Absolute,Y | LDA Oper,Y | B9 | 3 | 4* |
| (Indirect,X) | LDA (Oper,X) | A1 | 2 | 6 |
| (Indirect),Y | LDA (Oper),Y | B1 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
LDX LDX Load index X with memory LDX
Operation: M -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.0)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDX #Oper | A2 | 2 | 2 |
| Zero Page | LDX Oper | A6 | 2 | 3 |
| Zero Page,Y | LDX Oper,Y | B6 | 2 | 4 |
| Absolute | LDX Oper | AE | 3 | 4 |
| Absolute,Y | LDX Oper,Y | BE | 3 | 4* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
LDY LDY Load index Y with memory LDY
N Z C I D V
Operation: M -> Y / / _ _ _ _
(Ref: 7.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDY #Oper | A0 | 2 | 2 |
| Zero Page | LDY Oper | A4 | 2 | 3 |
| Zero Page,X | LDY Oper,X | B4 | 2 | 4 |
| Absolute | LDY Oper | AC | 3 | 4 |
| Absolute,X | LDY Oper,X | BC | 3 | 4* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
LSR LSR Shift right one bit (memory or accumulator) LSR
+-+-+-+-+-+-+-+-+
Operation: 0 -> |7|6|5|4|3|2|1|0| -> C N Z C I D V
+-+-+-+-+-+-+-+-+ 0 / / _ _ _
(Ref: 10.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | LSR A | 4A | 1 | 2 |
| Zero Page | LSR Oper | 46 | 2 | 5 |
| Zero Page,X | LSR Oper,X | 56 | 2 | 6 |
| Absolute | LSR Oper | 4E | 3 | 6 |
| Absolute,X | LSR Oper,X | 5E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
NOP NOP No operation NOP
N Z C I D V
Operation: No Operation (2 cycles) _ _ _ _ _ _
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | NOP | EA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
ORA ORA "OR" memory with accumulator ORA
Operation: A V M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | ORA #Oper | 09 | 2 | 2 |
| Zero Page | ORA Oper | 05 | 2 | 3 |
| Zero Page,X | ORA Oper,X | 15 | 2 | 4 |
| Absolute | ORA Oper | 0D | 3 | 4 |
| Absolute,X | ORA Oper,X | 10 | 3 | 4* |
| Absolute,Y | ORA Oper,Y | 19 | 3 | 4* |
| (Indirect,X) | ORA (Oper,X) | 01 | 2 | 6 |
| (Indirect),Y | ORA (Oper),Y | 11 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 on page crossing
PHA PHA Push accumulator on stack PHA
Operation: A toS N Z C I D V
_ _ _ _ _ _
(Ref: 8.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PHA | 48 | 1 | 3 |
+----------------+-----------------------+---------+---------+----------+
PHP PHP Push processor status on stack PHP
Operation: P toS N Z C I D V
_ _ _ _ _ _
(Ref: 8.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PHP | 08 | 1 | 3 |
+----------------+-----------------------+---------+---------+----------+
PLA PLA Pull accumulator from stack PLA
Operation: A fromS N Z C I D V
_ _ _ _ _ _
(Ref: 8.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PLA | 68 | 1 | 4 |
+----------------+-----------------------+---------+---------+----------+
PLP PLP Pull processor status from stack PLA
Operation: P fromS N Z C I D V
From Stack
(Ref: 8.12)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PLP | 28 | 1 | 4 |
+----------------+-----------------------+---------+---------+----------+
ROL ROL Rotate one bit left (memory or accumulator) ROL
+------------------------------+
| M or A |
| +-+-+-+-+-+-+-+-+ +-+ |
Operation: +-< |7|6|5|4|3|2|1|0| <- |C| <-+ N Z C I D V
+-+-+-+-+-+-+-+-+ +-+ / / / _ _ _
(Ref: 10.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ROL A | 2A | 1 | 2 |
| Zero Page | ROL Oper | 26 | 2 | 5 |
| Zero Page,X | ROL Oper,X | 36 | 2 | 6 |
| Absolute | ROL Oper | 2E | 3 | 6 |
| Absolute,X | ROL Oper,X | 3E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
ROR ROR Rotate one bit right (memory or accumulator) ROR
+------------------------------+
| |
| +-+ +-+-+-+-+-+-+-+-+ |
Operation: +-> |C| -> |7|6|5|4|3|2|1|0| >-+ N Z C I D V
+-+ +-+-+-+-+-+-+-+-+ / / / _ _ _
(Ref: 10.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ROR A | 6A | 1 | 2 |
| Zero Page | ROR Oper | 66 | 2 | 5 |
| Zero Page,X | ROR Oper,X | 76 | 2 | 6 |
| Absolute | ROR Oper | 6E | 3 | 6 |
| Absolute,X | ROR Oper,X | 7E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
Note: ROR instruction is available on MCS650X microprocessors after
June, 1976.
RTI RTI Return from interrupt RTI
N Z C I D V
Operation: P fromS PC fromS From Stack
(Ref: 9.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | RTI | 4D | 1 | 6 |
+----------------+-----------------------+---------+---------+----------+
RTS RTS Return from subroutine RTS
N Z C I D V
Operation: PC fromS, PC + 1 -> PC _ _ _ _ _ _
(Ref: 8.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | RTS | 60 | 1 | 6 |
+----------------+-----------------------+---------+---------+----------+
SBC SBC Subtract memory from accumulator with borrow SBC
-
Operation: A - M - C -> A N Z C I D V
- / / / _ _ /
Note:C = Borrow (Ref: 2.2.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | SBC #Oper | E9 | 2 | 2 |
| Zero Page | SBC Oper | E5 | 2 | 3 |
| Zero Page,X | SBC Oper,X | F5 | 2 | 4 |
| Absolute | SBC Oper | ED | 3 | 4 |
| Absolute,X | SBC Oper,X | FD | 3 | 4* |
| Absolute,Y | SBC Oper,Y | F9 | 3 | 4* |
| (Indirect,X) | SBC (Oper,X) | E1 | 2 | 6 |
| (Indirect),Y | SBC (Oper),Y | F1 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
SEC SEC Set carry flag SEC
Operation: 1 -> C N Z C I D V
_ _ 1 _ _ _
(Ref: 3.0.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SEC | 38 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
SED SED Set decimal mode SED
N Z C I D V
Operation: 1 -> D _ _ _ _ 1 _
(Ref: 3.3.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SED | F8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
SEI SEI Set interrupt disable status SED
N Z C I D V
Operation: 1 -> I _ _ _ 1 _ _
(Ref: 3.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SEI | 78 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
STA STA Store accumulator in memory STA
Operation: A -> M N Z C I D V
_ _ _ _ _ _
(Ref: 2.1.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STA Oper | 85 | 2 | 3 |
| Zero Page,X | STA Oper,X | 95 | 2 | 4 |
| Absolute | STA Oper | 80 | 3 | 4 |
| Absolute,X | STA Oper,X | 90 | 3 | 5 |
| Absolute,Y | STA Oper, Y | 99 | 3 | 5 |
| (Indirect,X) | STA (Oper,X) | 81 | 2 | 6 |
| (Indirect),Y | STA (Oper),Y | 91 | 2 | 6 |
+----------------+-----------------------+---------+---------+----------+
STX STX Store index X in memory STX
Operation: X -> M N Z C I D V
_ _ _ _ _ _
(Ref: 7.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STX Oper | 86 | 2 | 3 |
| Zero Page,Y | STX Oper,Y | 96 | 2 | 4 |
| Absolute | STX Oper | 8E | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
STY STY Store index Y in memory STY
Operation: Y -> M N Z C I D V
_ _ _ _ _ _
(Ref: 7.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STY Oper | 84 | 2 | 3 |
| Zero Page,X | STY Oper,X | 94 | 2 | 4 |
| Absolute | STY Oper | 8C | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
TAX TAX Transfer accumulator to index X TAX
Operation: A -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TAX | AA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TAY TAY Transfer accumulator to index Y TAY
Operation: A -> Y N Z C I D V
/ / _ _ _ _
(Ref: 7.13)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TAY | A8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TSX TSX Transfer stack pointer to index X TSX
Operation: S -> X N Z C I D V
/ / _ _ _ _
(Ref: 8.9)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TSX | BA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TXA TXA Transfer index X to accumulator TXA
N Z C I D V
Operation: X -> A / / _ _ _ _
(Ref: 7.12)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TXA | 8A | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TXS TXS Transfer index X to stack pointer TXS
N Z C I D V
Operation: X -> S _ _ _ _ _ _
(Ref: 8.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TXS | 9A | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TYA TYA Transfer index Y to accumulator TYA
Operation: Y -> A N Z C I D V
/ / _ _ _ _
(Ref: 7.14)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TYA | 98 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
+------------------------------------------------------------------------
| INSTRUCTION ADDRESSING MODES AND RELATED EXECUTION TIMES
| (in clock cycles)
+------------------------------------------------------------------------
A A A B B B B B B B B B B C
D N S C C E I M N P R V V L
C D L C S Q T I E L K C S C
Accumulator | . . 2 . . . . . . . . . . .
Immediate | 2 2 . . . . . . . . . . .
Zero Page | 3 3 5 . . . 3 . . . . . . .
Zero Page,X | 4 4 6 . . . . . . . . . . .
Zero Page,Y | . . . . . . . . . . . . . .
Absolute | 4 4 6 . . . 4 . . . . . . .
Absolute,X | 4* 4* 7 . . . . . . . . . . .
Absolute,Y | 4* 4* . . . . . . . . . . . .
Implied | . . . . . . . . . . . . . 2
Relative | . . . 2** 2** 2** . 2** 2** 2** 7 2** 2** .
(Indirect,X) | 6 6 . . . . . . . . . . . .
(Indirect),Y | 5* 5* . . . . . . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
C C C C C C D D D E I I I J
L L L M P P E E E O N N N M
D I V P X Y C X Y R C X Y P
Accumulator | . . . . . . . . . . . . . .
Immediate | . . . 2 2 2 . . . 2 . . . .
Zero Page | . . . 3 3 3 5 . . 3 5 . . .
Zero Page,X | . . . 4 . . 6 . . 4 6 . . .
Zero Page,Y | . . . . . . . . . . . . . .
Absolute | . . . 4 4 4 6 . . 4 6 . . 3
Absolute,X | . . . 4* . . 7 . . 4* 7 . . .
Absolute,Y | . . . 4* . . . . . 4* . . . .
Implied | 2 2 2 . . . . 2 2 . . 2 2 .
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . . . 6 . . . . . 6 . . . .
(Indirect),Y | . . . 5* . . . . . 5* . . . .
Abs. Indirect| . . . . . . . . . . . . . 5
+-----------------------------------------------------------
* Add one cycle if indexing across page boundary
** Add one cycle if branch is taken, Add one additional if branching
operation crosses page boundary
------------------------------------------------------------------------+
INSTRUCTION ADDRESSING MODES AND RELATED EXECUTION TIMES |
(in clock cycles) |
------------------------------------------------------------------------+
J L L L L N O P P P P R R R
S D D D S O R H H L L O O T
R A X Y R P A A P A P L R I
Accumulator | . . . . 2 . . . . . . 2 2 .
Immediate | . 2 2 2 . . 2 . . . . . . .
Zero Page | . 3 3 3 5 . 3 . . . . 5 5 .
Zero Page,X | . 4 . 4 6 . 4 . . . . 6 6 .
Zero Page,Y | . . 4 . . . . . . . . . . .
Absolute | 6 4 4 4 6 . 4 . . . . 6 6 .
Absolute,X | . 4* . 4* 7 . 4* . . . . 7 7 .
Absolute,Y | . 4* 4* . . . 4* . . . . . . .
Implied | . . . . . 2 . 3 3 4 4 . . 6
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . 6 . . . . 6 . . . . . . .
(Indirect),Y | . 5* . . . . 5* . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
R S S S S S S S T T T T T T
T B E E E T T T A A S X X Y
S C C D I A X Y X Y X A S A
Accumulator | . . . . . . . . . . . . . .
Immediate | . 2 . . . . . . . . . . . .
Zero Page | . 3 . . . 3 3 3 . . . . . .
Zero Page,X | . 4 . . . 4 . 4 . . . . . .
Zero Page,Y | . . . . . . 4 . . . . . . .
Absolute | . 4 . . . 4 4 4 . . . . . .
Absolute,X | . 4* . . . 5 . . . . . . . .
Absolute,Y | . 4* . . . 5 . . . . . . . .
Implied | 6 . 2 2 2 . . . 2 2 2 2 2 2
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . 6 . . . 6 . . . . . . . .
(Indirect),Y | . 5* . . . 6 . . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
* Add one cycle if indexing across page boundary
** Add one cycle if branch is taken, Add one additional if branching
operation crosses page boundary
00 - BRK 20 - JSR
01 - ORA - (Indirect,X) 21 - AND - (Indirect,X)
02 - Future Expansion 22 - Future Expansion
03 - Future Expansion 23 - Future Expansion
04 - Future Expansion 24 - BIT - Zero Page
05 - ORA - Zero Page 25 - AND - Zero Page
06 - ASL - Zero Page 26 - ROL - Zero Page
07 - Future Expansion 27 - Future Expansion
08 - PHP 28 - PLP
09 - ORA - Immediate 29 - AND - Immediate
0A - ASL - Accumulator 2A - ROL - Accumulator
0B - Future Expansion 2B - Future Expansion
0C - Future Expansion 2C - BIT - Absolute
0D - ORA - Absolute 2D - AND - Absolute
0E - ASL - Absolute 2E - ROL - Absolute
0F - Future Expansion 2F - Future Expansion
10 - BPL 30 - BMI
11 - ORA - (Indirect),Y 31 - AND - (Indirect),Y
12 - Future Expansion 32 - Future Expansion
13 - Future Expansion 33 - Future Expansion
14 - Future Expansion 34 - Future Expansion
15 - ORA - Zero Page,X 35 - AND - Zero Page,X
16 - ASL - Zero Page,X 36 - ROL - Zero Page,X
17 - Future Expansion 37 - Future Expansion
18 - CLC 38 - SEC
19 - ORA - Absolute,Y 39 - AND - Absolute,Y
1A - Future Expansion 3A - Future Expansion
1B - Future Expansion 3B - Future Expansion
1C - Future Expansion 3C - Future Expansion
1D - ORA - Absolute,X 3D - AND - Absolute,X
1E - ASL - Absolute,X 3E - ROL - Absolute,X
1F - Future Expansion 3F - Future Expansion
40 - RTI 60 - RTS
41 - EOR - (Indirect,X) 61 - ADC - (Indirect,X)
42 - Future Expansion 62 - Future Expansion
43 - Future Expansion 63 - Future Expansion
44 - Future Expansion 64 - Future Expansion
45 - EOR - Zero Page 65 - ADC - Zero Page
46 - LSR - Zero Page 66 - ROR - Zero Page
47 - Future Expansion 67 - Future Expansion
48 - PHA 68 - PLA
49 - EOR - Immediate 69 - ADC - Immediate
4A - LSR - Accumulator 6A - ROR - Accumulator
4B - Future Expansion 6B - Future Expansion
4C - JMP - Absolute 6C - JMP - Indirect
4D - EOR - Absolute 6D - ADC - Absolute
4E - LSR - Absolute 6E - ROR - Absolute
4F - Future Expansion 6F - Future Expansion
50 - BVC 70 - BVS
51 - EOR - (Indirect),Y 71 - ADC - (Indirect),Y
52 - Future Expansion 72 - Future Expansion
53 - Future Expansion 73 - Future Expansion
54 - Future Expansion 74 - Future Expansion
55 - EOR - Zero Page,X 75 - ADC - Zero Page,X
56 - LSR - Zero Page,X 76 - ROR - Zero Page,X
57 - Future Expansion 77 - Future Expansion
58 - CLI 78 - SEI
59 - EOR - Absolute,Y 79 - ADC - Absolute,Y
5A - Future Expansion 7A - Future Expansion
5B - Future Expansion 7B - Future Expansion
5C - Future Expansion 7C - Future Expansion
50 - EOR - Absolute,X 70 - ADC - Absolute,X
5E - LSR - Absolute,X 7E - ROR - Absolute,X
5F - Future Expansion 7F - Future Expansion
80 - Future Expansion A0 - LDY - Immediate
81 - STA - (Indirect,X) A1 - LDA - (Indirect,X)
82 - Future Expansion A2 - LDX - Immediate
83 - Future Expansion A3 - Future Expansion
84 - STY - Zero Page A4 - LDY - Zero Page
85 - STA - Zero Page A5 - LDA - Zero Page
86 - STX - Zero Page A6 - LDX - Zero Page
87 - Future Expansion A7 - Future Expansion
88 - DEY A8 - TAY
89 - Future Expansion A9 - LDA - Immediate
8A - TXA AA - TAX
8B - Future Expansion AB - Future Expansion
8C - STY - Absolute AC - LDY - Absolute
80 - STA - Absolute AD - LDA - Absolute
8E - STX - Absolute AE - LDX - Absolute
8F - Future Expansion AF - Future Expansion
90 - BCC B0 - BCS
91 - STA - (Indirect),Y B1 - LDA - (Indirect),Y
92 - Future Expansion B2 - Future Expansion
93 - Future Expansion B3 - Future Expansion
94 - STY - Zero Page,X B4 - LDY - Zero Page,X
95 - STA - Zero Page,X BS - LDA - Zero Page,X
96 - STX - Zero Page,Y B6 - LDX - Zero Page,Y
97 - Future Expansion B7 - Future Expansion
98 - TYA B8 - CLV
99 - STA - Absolute,Y B9 - LDA - Absolute,Y
9A - TXS BA - TSX
9B - Future Expansion BB - Future Expansion
9C - Future Expansion BC - LDY - Absolute,X
90 - STA - Absolute,X BD - LDA - Absolute,X
9E - Future Expansion BE - LDX - Absolute,Y
9F - Future Expansion BF - Future Expansion
C0 - Cpy - Immediate E0 - CPX - Immediate
C1 - CMP - (Indirect,X) E1 - SBC - (Indirect,X)
C2 - Future Expansion E2 - Future Expansion
C3 - Future Expansion E3 - Future Expansion
C4 - CPY - Zero Page E4 - CPX - Zero Page
C5 - CMP - Zero Page E5 - SBC - Zero Page
C6 - DEC - Zero Page E6 - INC - Zero Page
C7 - Future Expansion E7 - Future Expansion
C8 - INY E8 - INX
C9 - CMP - Immediate E9 - SBC - Immediate
CA - DEX EA - NOP
CB - Future Expansion EB - Future Expansion
CC - CPY - Absolute EC - CPX - Absolute
CD - CMP - Absolute ED - SBC - Absolute
CE - DEC - Absolute EE - INC - Absolute
CF - Future Expansion EF - Future Expansion
D0 - BNE F0 - BEQ
D1 - CMP (Indirect@,Y F1 - SBC - (Indirect),Y
D2 - Future Expansion F2 - Future Expansion
D3 - Future Expansion F3 - Future Expansion
D4 - Future Expansion F4 - Future Expansion
D5 - CMP - Zero Page,X F5 - SBC - Zero Page,X
D6 - DEC - Zero Page,X F6 - INC - Zero Page,X
D7 - Future Expansion F7 - Future Expansion
D8 - CLD F8 - SED
D9 - CMP - Absolute,Y F9 - SBC - Absolute,Y
DA - Future Expansion FA - Future Expansion
DB - Future Expansion FB - Future Expansion
DC - Future Expansion FC - Future Expansion
DD - CMP - Absolute,X FD - SBC - Absolute,X
DE - DEC - Absolute,X FE - INC - Absolute,X
DF - Future Expansion FF - Future Expansion
INSTRUCTION OPERATION
The following code has been taken from VICE for the purposes of showing
how each instruction operates. No particular addressing mode is used since
we only wish to see the operation of the instruction itself.
src : the byte of data that is being addressed.
SET_SIGN : sets\resets the sign flag depending on bit 7.
SET_ZERO : sets\resets the zero flag depending on whether the result
is zero or not.
SET_CARRY(condition) : if the condition has a non-zero value then the
carry flag is set, else it is reset.
SET_OVERFLOW(condition) : if the condition is true then the overflow
flag is set, else it is reset.
SET_INTERRUPT : }
SET_BREAK : } As for SET_CARRY and SET_OVERFLOW.
SET_DECIMAL : }
REL_ADDR(PC, src) : returns the relative address obtained by adding
the displacement src to the PC.
SET_SR : set the Program Status Register to the value given.
GET_SR : get the value of the Program Status Register.
PULL : Pull a byte off the stack.
PUSH : Push a byte onto the stack.
LOAD : Get a byte from the memory address.
STORE : Store a byte in a memory address.
IF_CARRY, IF_OVERFLOW, IF_SIGN, IF_ZERO etc : Returns true if the
relevant flag is set, otherwise returns false.
clk : the number of cycles an instruction takes. This is shown below
in situations where the number of cycles changes depending
on the result of the instruction (eg. Branching instructions).
AC = Accumulator
XR = X register
YR = Y register
PC = Program Counter
SP = Stack Pointer
/* ADC */
unsigned int temp = src + AC + (IF_CARRY() ? 1 : 0);
SET_ZERO(temp & 0xff); /* This is not valid in decimal mode */
if (IF_DECIMAL()) {
if (((AC & 0xf) + (src & 0xf) + (IF_CARRY() ? 1 : 0)) > 9) temp += 6;
SET_SIGN(temp);
SET_OVERFLOW(!((AC ^ src) & 0x80) && ((AC ^ temp) & 0x80));
if (temp > 0x99) temp += 96;
SET_CARRY(temp > 0x99);
} else {
SET_SIGN(temp);
SET_OVERFLOW(!((AC ^ src) & 0x80) && ((AC ^ temp) & 0x80));
SET_CARRY(temp > 0xff);
}
AC = ((BYTE) temp);
/* AND */
src &= AC;
SET_SIGN(src);
SET_ZERO(src);
AC = src;
/* ASL */
SET_CARRY(src & 0x80);
src <<= 1;
src &= 0xff;
SET_SIGN(src);
SET_ZERO(src);
STORE src in memory or accumulator depending on addressing mode.
/* BCC */
if (!IF_CARRY()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BCS */
if (IF_CARRY()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BEQ */
if (IF_ZERO()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BIT */
SET_SIGN(src);
SET_OVERFLOW(0x40 & src); /* Copy bit 6 to OVERFLOW flag. */
SET_ZERO(src & AC);
/* BMI */
if (IF_SIGN()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BNE */
if (!IF_ZERO()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BPL */
if (!IF_SIGN()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BRK */
PC++;
PUSH((PC >> 8) & 0xff); /* Push return address onto the stack. */
PUSH(PC & 0xff);
SET_BREAK((1)); /* Set BFlag before pushing */
PUSH(SR);
SET_INTERRUPT((1));
PC = (LOAD(0xFFFE) | (LOAD(0xFFFF) << 8));
/* BVC */
if (!IF_OVERFLOW()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BVS */
if (IF_OVERFLOW()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* CLC */
SET_CARRY((0));
/* CLD */
SET_DECIMAL((0));
/* CLI */
SET_INTERRUPT((0));
/* CLV */
SET_OVERFLOW((0));
/* CMP */
src = AC - src;
SET_CARRY(src < 0x100);
SET_SIGN(src);
SET_ZERO(src &= 0xff);
/* CPX */
src = XR - src;
SET_CARRY(src < 0x100);
SET_SIGN(src);
SET_ZERO(src &= 0xff);
/* CPY */
src = YR - src;
SET_CARRY(src < 0x100);
SET_SIGN(src);
SET_ZERO(src &= 0xff);
/* DEC */
src = (src - 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
STORE(address, (src));
/* DEX */
unsigned src = XR;
src = (src - 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* DEY */
unsigned src = YR;
src = (src - 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
YR = (src);
/* EOR */
src ^= AC;
SET_SIGN(src);
SET_ZERO(src);
AC = src;
/* INC */
src = (src + 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
STORE(address, (src));
/* INX */
unsigned src = XR;
src = (src + 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* INY */
unsigned src = YR;
src = (src + 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
YR = (src);
/* JMP */
PC = (src);
/* JSR */
PC--;
PUSH((PC >> 8) & 0xff); /* Push return address onto the stack. */
PUSH(PC & 0xff);
PC = (src);
/* LDA */
SET_SIGN(src);
SET_ZERO(src);
AC = (src);
/* LDX */
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* LDY */
SET_SIGN(src);
SET_ZERO(src);
YR = (src);
/* LSR */
SET_CARRY(src & 0x01);
src >>= 1;
SET_SIGN(src);
SET_ZERO(src);
STORE src in memory or accumulator depending on addressing mode.
/* NOP */
Nothing.
/* ORA */
src |= AC;
SET_SIGN(src);
SET_ZERO(src);
AC = src;
/* PHA */
src = AC;
PUSH(src);
/* PHP */
src = GET_SR;
PUSH(src);
/* PLA */
src = PULL();
SET_SIGN(src); /* Change sign and zero flag accordingly. */
SET_ZERO(src);
/* PLP */
src = PULL();
SET_SR((src));
/* ROL */
src <<= 1;
if (IF_CARRY()) src |= 0x1;
SET_CARRY(src > 0xff);
src &= 0xff;
SET_SIGN(src);
SET_ZERO(src);
STORE src in memory or accumulator depending on addressing mode.
/* ROR */
if (IF_CARRY()) src |= 0x100;
SET_CARRY(src & 0x01);
src >>= 1;
SET_SIGN(src);
SET_ZERO(src);
STORE src in memory or accumulator depending on addressing mode.
/* RTI */
src = PULL();
SET_SR(src);
src = PULL();
src |= (PULL() << 8); /* Load return address from stack. */
PC = (src);
/* RTS */
src = PULL();
src += ((PULL()) << 8) + 1; /* Load return address from stack and add 1. */
PC = (src);
/* SBC */
unsigned int temp = AC - src - (IF_CARRY() ? 0 : 1);
SET_SIGN(temp);
SET_ZERO(temp & 0xff); /* Sign and Zero are invalid in decimal mode */
SET_OVERFLOW(((AC ^ temp) & 0x80) && ((AC ^ src) & 0x80));
if (IF_DECIMAL()) {
if ( ((AC & 0xf) - (IF_CARRY() ? 0 : 1)) < (src & 0xf)) /* EP */ temp -= 6;
if (temp > 0x99) temp -= 0x60;
}
SET_CARRY(temp < 0x100);
AC = (temp & 0xff);
/* SEC */
SET_CARRY((1));
/* SED */
SET_DECIMAL((1));
/* SEI */
SET_INTERRUPT((1));
/* STA */
STORE(address, (src));
/* STX */
STORE(address, (src));
/* STY */
STORE(address, (src));
/* TAX */
unsigned src = AC;
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* TAY */
unsigned src = AC;
SET_SIGN(src);
SET_ZERO(src);
YR = (src);
/* TSX */
unsigned src = SP;
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* TXA */
unsigned src = XR;
SET_SIGN(src);
SET_ZERO(src);
AC = (src);
/* TXS */
unsigned src = XR;
SP = (src);
/* TYA */
unsigned src = YR;
SET_SIGN(src);
SET_ZERO(src);
AC = (src);