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From: Erick Wagner <wagnere@netcom.com>
Newsgroups: comp.sys.apple2.programmer
Subject: Re: Q: I/O 32 card from Applied Engineering
Date: 5 Dec 1995 15:53:02 GMT
Organization: PRC
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Recently Dave Lyons and John Bowling asked about the AE I/O 32 card.
I sent Dave some info via email but thought I should post so others
could benefit from it too.
>I suspect that the AE card used a couple of 6522's
Good guess but wrong :) AE used a pair of Motorola 6821 chips.
MicroDimensions also used the 6821 chip in at least one of their
I/O boards and the John Bell Engineering board uses the 6522. If you
have a choice over which I/O to use, I'd lean towards the 6522. It
seems to be a little more straightforward in terms of setting it up
for I/O and it has some wonderful built-in timers that can prevent
you from writing some fairly complex code.
Well, here's the info I sent to Dave:
======================================
Applied Engineering I/O 32 Information
======================================
If a bit in the Data Direction Register is 1, the
corresponding bit of the Port is an output; otherwise,
it is an input.
The procedure for writing to an output is:
(1) Write a 0 to bit 2 of the Control Register
(2) Write 1's to the Data Direction Register of each
output bit
(3) Write a 1 to bit 2 of the Control Register
(4) Write data to the Port
The procedure for reading to an input is:
(1) Write a 0 to bit 2 of the Control Register
(2) Write 0's to the Data Direction Register of each
input bit
(3) Write a 1 to bit 2 of the Control Register
(4) Read data from the Port
Control Register A $C085+s0
Control Register B $C087+s0
Control Register C $C089+s0
Control Register D $C08B+s0
Examples:
Reading all 8 bits from Port A
LDA $C085+s0 ;Read Control Register A
AND #%11111011 ;Turn off bit 2
STA $C085+s0 ;Set CRA for Data Direction
LDX #$00 ;All bits are inputs
STX $C084+s0 ;Set Data Direction for all inputs
ORA #%00000100 ;Turn on bit 2
STA $C085+s0 ;Set CRA for Port A data
LDA $C084+s0 ;Read Port A data
Reading bits 0, 1, 2 from Port B
LDA $C087+s0 ;Read Control Register B
AND #%11111011 ;Turn off bit 2
STA $C087+s0 ;Set CRB for Data Direction
LDX #%11111000 ;Bits 0, 1, 2 are inputs
STX $C086+s0 ;Set Data Direction
ORA #%00000100 ;Turn on bit 2
STA $C087+s0 ;Set CRB for Port B data
LDA $C086+s0 ;Read Port B data
Writing bits 4, 5, 6, 7 to Port C
LDA $C089+s0 ;Read Control Register C
AND #%11111011 ;Turn off bit 2
STA $C089+s0 ;Set CRC for Data Direction
LDX #%11110000 ;Bits 4, 5, 6, 7 are outputs
STX $C088+s0 ;Set Data Direction
ORA #%00000100 ;Turn on bit 2
STA $C089+s0 ;Set CRC for Port C data
LDA #$A0 ;Data to write
STA $C088+s0 ;Write Port C data
Writing all 8 bits to Port D
LDA $C08B+s0 ;Read Control Register D
AND #%11111011 ;Turn off bit 2
STA $C08B+s0 ;Set CRD for Data Direction
LDX #$FF ;All bits are outputs
STX $C08A+s0 ;Set Data Direction for all outputs
ORA #%00000100 ;Turn on bit 2
STA $C08B+s0 ;Set CRD for Port D data
LDA #$AE ;Data to write
STA $C08A+s0 ;Write Port D data
[end of document]