The Programmer's Guide to TRSDOS Version 6 - Tim Mann's Home ...

Note: @EXIT in SYS1 automatically restores BREAK to the system handler. This is
not done for @CMNDR. Also, don't forget that if DEBUG is enabled, then entry to
DEBUG takes precedence over the BREAK (of course, even though DEBUG has been
enabled, if you only have EXEC access, DEBUG is effectively disabled).
Your break handling routine will need to debounce the BREAK key and obviously deal
with the stack pointer (since the stack could be anywhere depending on when and
where the break was detected). Something of the following is suitable:
ENTRY LD (STKSAV),SP ;Save the stack pointer
PUSH HL
LD HL,MYBRK ;Point to your BREAK handler
@@BREAK ;Set up "MYBRK" as break entry
.
.
MYBRK DI ;Don't permit further BREAKs
LD B,80H ;Wait for fingers to get off
@@PAUSE ; of the BREAK key
LD SP,$-$ ;P/u the orig stack pointer
STKSAV EQU $-2
EI ;Interrupts back on
what ever you want
RET ;To what invoked the program
7.6.6 @CHNIO SVC-20
This SVC is used to pass control to the next module in a device chain. Its use is
restricted to device filters. Detailed information on the use of @CHNIO will be found in
chapter 3, DEVICE INPUT/OUTPUT INTERFACING.
Registers Affected: Depends on the filter modules chained.
Entry:
IX Contains a pointer to the Device Control Block assigned to the filter
module. This is recovered from the MODDCB field located in the module
header. Note: IX should be saved before loading and restored upon return
from @CHNIO.
B Contains the I/O direction code (GET=1, PUT=2, CTL=4).
C Contains the output character for PUT or GET.
7.6.7 @CKBRKC SVC-106
This SVC was installed effective release 6.2.0. It checks to see if the BREAK key has
been pressed. It also clears the BREAK bit of the KFLAG$ if a break condition is
detected.
Registers Affected: AF.
Exit:
Z BREAK was not detected.
NZ BREAK was detected. SVC returns only when BREAK is released.
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