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Model 100 Hints and Tips
The following is a series of "hints and tricks" for getting the most out of the TRS-80 Model 100.
This file is intended to become an ongoing 'mini-magazine' within this SIG. Plans for future updates include
deciphering some ROM code for use within BASIC and Machine Language programs.
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* "Printer Not Ready"
There is a problem within the TRS-80 Model 100 that makes the machine seem to "hang". This is usually caused by pressing
the PRINT key, which attempts to copy the contents of the non-graphic Model 100 screen to an attached printer. The problem
manifests itself if there is no printer attached.
Additionally, this can be caused by a BASIC or Machine Language (M/L) program, or one of the ROM programs TEXT, TELCOM,
SCHEDL, and ADDRSS attempting to output to a non-existant printer.
Usually, pressing SHIFT-BREAK will produce an "aborted" message within a ROM program, or "?IO Error" within a BASIC
program. If a machine language program is executing and the (non-documented) error vector is not 'plugged', an "?IO Error"
will be generated and a return will be made to BASIC.
Disabling the PRINT key is touchy at best. Actually, it is possible to disable the key, and all the 'miniature' keys
immediately underneath the display (F1-F8, PASTE, LABEL, PAUSE/ BREAK, etc.). In my opinion, though, the loss of the
function keys is greater than the problem of the PRINT key.
Since there is no easy, '1-poke' method of totazlly disabling the printer in the Model 100, we must be satisfied with the
"?IO Error" in BASIC (unless it is trapped with an ON ERROR statement). On the other hand, there is a simple way in
Machine Language or BASIC to tell if there is a printer attached.
BASIC
IF (INP(187)AND6)<>2 THEN PRINT"Not Ready"
Z80 Assembly Language:
PUSH BC ;Save BC
LD B,A ;Save A Reg
IN A,(0BBH) ;Get printer status
AND 06H ;Mask off non-status
XOR 02H ;Set flag bits
LD A,B ;Restore A Reg
POP BC ;Restore BC
JP NZ,NOTRDY ;Not ready if Non-Zero ...
;Printer Ready if code falls
;through
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The PASTE buffer has been documented by more than one program (although NOT by Radio Shack!) to reside at the address at
F88CH-F88DH (63628-63629 decimal). This address is stored in typical 8080 LSB/MSB format. What isn't so well documented is
that the two bytes preceding that address F88A-F88BH (63630-63631 decimal) contain the pointer to the text returned by
pressing the SHIFT and PRINT keys simultaneously. (In BASIC, SHIFT-PRINT points to the text "llist" followed by a carriage
return in ROM... try it!) Both of these "buffers" are terminated by a null byte, or CHR$(0). The SHIFT-PRINT key can thus
be useful in both BASIC and Machine Language programs.
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* "Carrier Detect in Basic"
A useful routine has been uploaded to the SIG called DIALER.100 and was submitted by Jerry Kohl [71256,23]. It is heavily
commented and explains a useful application of a routine that "times out" if carrier is not detected within a given amount
of time. The routine also contains an npublished entry point to TERM mode within TELCOM without losing carrier.
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* Tandy BUG Department:
The CHKDC ROM Call documented by Tandy at 5AA9H contains a "small" bug. It seems that the routine was actually written for
the ADRSS and SCHEDL ROM programs to search for ADRS.DO and NOTE.DO. The limitation here is that the routine will only
work if the filename being searched for contains 4 characters or less in the file name (preceding the required ".").
How to get around this problem:
The solution is really quite simple, just load the A register with 10 (Hex 0A) and enter the routine at the addess 5AABH.
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* What is the Shack up to next?
I have heard from more than one source that the price cut we saw on the Model 100 a couple of months ago is going to be
repeated sometime at the end of March or beginning of April.
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* BREAK key disable
Disabling the BREAK key can be accomplished by POKEing a value of 128 into the reserved RAM location 63056 (Hex F650).
This effectively eliminates all of the top row of keys (function keys, etc.). To re-enable, just POKE the value 0 back
into the same location.
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Model 100 ROM Calls
This article is number two in the "hints and tricks" article for getting the most out of your Model 100. The topic of this
particular session will be .
Radio Shack has been kind enough to document quite a few ROM calls, but they do not state that these entry points are
inviolate (ie. will not change with a new ROM revision), nor do they give too much information regarding how to use them
in BASIC programs.
The following is a series of ROM calls that can be used in to perform some odds and ends. To facilitate using some of the
more "esoteric" calls, I will also be providing a method of providing an "interface" to BASIC variables.
First, however, we will discuss the DOCUMENTED (by Tandy) ROM Calls that can be used directly in BASIC:
DISC: 52BBH (21179 Decimal) Disconnect Phone Line
This ROM Call will cause the internal modem to disconnect from the phone line.
Typical BASIC Usage:
CALL 21179
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CONN: 52D0H (21200) Pick up phone line
This ROM Call will cause the internal modem to "pick up" the phone line. This would be used when trying to detect if
carrier is present (see CARDET), but has other uses. A crude "dialing" mechanism could be done using the DISC and CONN ROM
Calls to "pulse" the phone line. In fact, this is how the Model 100 actually dials!
Typical BASIC usage:
CALL 21200
DIAL 532DH (21293) Dial phone number string @ (HL)
Here we come to the first ROM call that requires a parameter.
The call expects to find a valid phone number "string" (see manual on auto-dial strings) at the address pointed to by the
HL register. It is not documented, but the phone number must have a "terminator". This can either be a NULL CHR$(0), or an
"auto-log" string. If an auto-log string is used, the Model 100 will wait indefinitely for carrier before sending the
auto-log string.
Typical BASIC usage: (Autodialer)
PH$="555-1212" + CHR$(0) :' Phone Number in
PH$ V=VARPTR(PH$) :' Get addr of variable
AD!=PEEK(V+1) + PEEK(V+2)*256 :' Get addr of string
CALL 21293, 0, AD! :' Dial Phone Number
CALL 21200 :' Keep Phone line open
PRINT"Please pick up phone" :' Alert user
INPUT"Enter when ready"; A$ :' Wait till picked up
CALL 21179 :' Disconnect Model 100
(Auto-logon -- terminal program)
PH$="555-1212<=?U700000,0000^M?Ppsswrd^M?!G PCS154^M>" :' Phone Nbr + Auto Log
V=VARPTR(PH$) :' Get addr of variable
AD!=PEEK(V+1) + PEEK(V+2)*256 :' Get addr of string
CALL 21293, 0, AD! :' Dial and auto log OPEN "MDM:7I1E" FOR INPUT AS 1 :' Open up Modem...
OPEN "MDM:7I1E" FOR OUTPUT AS 2 :' for input and output ...
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CLRFLK 5A79H (23161) Clear function key definitions
This ROM Call would be useful for resetting ALL the function key definitions. It is not too useful for BASIC programs, but
it cannot be performed simillarly in a BASIC program (!).
Typical BASIC usage:
CALL 23161
STFNK 5A7CH (23164) Set function key table
CSFKEY 5B46H (23366) Cold Start Function key table address
BASFKY F80AH (63498 or -2308) Current function key def's used by BASIC
The STFNK call is often used in BASIC program to reset the function keys to their default cold start values. It can also
be used to set the keys to any value desired. The STFNK call requires the address of a table of function key values to be
stored at (HL), or the second argument to a CALL function.
Typical BASIC program -- Reset to Cold Start values:
CALL 23164, 0, 23366
Typical BASIC program -- Change keys and reset back:
A$="" :'Define a dummy string
V=VARPTR(A$) :'Get addr of variable
POKE V,128 :'128 characters long
POKE V+1,10 :'Point to...
POKE V+2,248 :'Current key def's
B$=A$ :'Store def's in B$
FOR X=16 TO 128 STEP 16 :'Set up delimiters
C=ASC(MID$(B$,X,1)) OR 128 :'Get delimiter
MID$(B$,X,1)=CHR$(C) :'Put it into string
NEXT X :'Continue
KEY 1, "F1" :'Now reset keys ... :'etc. at end of pgm:
V=VARPTR(B$) :'Get addr of variable
AD!=PEEK(V+1) + PEEK(V+2)*256 :'Get addr of key def's
CALL 23164, 0, AD! :'Reset key definitions
In the above example, the code up to the "KEY 1" statement is used to save the current function key settings into the
variable B$. The STFNK function call requires that the definitions for all the keys be "delimited" by setting the most
significant bit of the last byte. The FOR...NEXT loop performs this delimiting. At the end of the program, assuming that
the variable B$ has not been modified, the last three instructions are performed, which reset the function key definitions
to their original values.
RCVX 6D6DH (28013) Return number of characters in RS-232 queue in A
This ROM call is not too useful to be used directly in BASIC because BASIC has no way of returning values from ROM Calls.
But... we can create a machine language "front end" that will suffice nicely. You do not need to know machine language to
use this routine:
00
NOP ;Offset byte for call
CD 6D 6D
CALL RCVX ;Call routine 77
LD (HL),A ;Store value in variable 23
INC HL ;Bump pointer 36 00
LD (HL),00H ;Zero MSB C9
RET ;And return 00
NOP ;Offset bytes
The values on the left side of the listing above are the hexidecimal values of the assembly language instructions on the
right. These values can be "paired" off to be stored in an "integer array" as shown below. The decimal equivalent of the
integer pairs is shown to the right:
00 CD -13056
ML%(0) 6D 6D 28013
ML%(1) 66 23 9062
ML%(2) 36 00 54
ML%(3) C9 00 201
ML%(4)
Thus, if we set up this array at the start of the program:
DIM ML%(4) :' Reserve space
FOR X=0 TO 4 :' Four values
READ ML%(X) :' Store integer value
NEXT X :' Continue
DATA-31056,28013,9062,54,201 :' Data values
At this point, we now have a relocatable machine language routine of our own. What does it do?? It allows us to call a ROM
routine that returns a value in the A register, and get the value into an INTEGER variable in BASIC.
How? Let's say that we want to call this routine stored in ML%(0-4) and return the value in the BASIC variable CT%.
This would be accomplished as follows:
CT%=0 :' Define variable
CALL VARPTR(ML%(0)), 0, VARPTR(CT%) :' Do routine
PRINT CT% :' Print the count
Pretty simple, once it is implemented. The ML% array above is useful for other routines. All that need be changed is the
value in ML%(1), which should contain the address of the routine to be called.
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RV232C (6D7EH) (28030) Get character from RS-232 to A register
This routine is another that can be useful in BASIC in conjunction with the ML% array shown above. Change the value of
ML%(1) to 28030 by executing a statement like:
ML%(1) = 28030
And the ML% routine can be used to get a character from the RS-232 queue. The advantage of using this routine (as opposed
to the BASIC INPUT$ statement), is that ALL values passed from the RS-232 queue will be available. The INPUT$ statement
does not allow the value CHR$(127) or CHR$(26)... in fact, receiving CHR$(26) has the effect of CLOSING the RS-232 file!!
Typical BASIC program usage:
REM ML% Array set up with ML%(1) = 28030
CT% = 0 :' Initialize variable
CALL VARPTR(ML%(0)), 0, VARPTR(CT%) :' Do routine
PRINT CT% :' Print the char
SENDCQ 6E0BH (28171) Send XON Resume character
SENDCS 6E1EH (28190) Send XOFF Pause character
These two routines are usefull for pausing and resuming transmission from a host that acknowleges XON/XOFF protocol.
This can be useful for times when general "housekeeping" must be done. After an XOFF character (Pause) is sent, the host
should stop transmitting. At that point, the program can do what it needs to do, such as outputing to a slow device (such
as cassette), etc. When ready to resume transmission, send the XON character (Resume).
Typical BASIC usage:
CALL 28190 :'Send XOFF Pause
GOSUB --- :'Do interesting things
CALL 28171 :'Send XON Resume ... :'Continue receiving
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SD232C 6E23H (28195) Send character in A to RS-232 port
This routine can be used to send a single character to the RS-232 port. In all actuality, there is no real benefit to
using this call, as the PRINT # command allows you to send as many characters at a time as you wish with no restrictions.
Typical BASIC program usage:
CALL 28195, 3 :'Send ^C to HOST
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CARDET 6EEFH (28399) Return carrier detect status in A
Since this routine returns a value, it is necessary to use a machine language "front end". The ML% array described above
can be used if the statement:
ML%(1) = 28399
is executed. When the ML% routine is used to call the CARDET routine, the status returned is:
0 Carrier Detected
255 Carrier not found
Typical BASIC program usage:
REM ML% Array setup as described above
CD% = 0 :'Initialize variable
CALL VARPTR(ML%(0)), 0, VARPTR(CD%) :'Get carrier status
IF CD% = 0 THEN PRINT"CARRIER DETECTED" ELSE PRINT"NO CARRIER"
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Look for other exciting installments in the near future.
Comments and/or suggestions are welcome. Send them to larry gensch [72236,3516]