Hello,

I've been having problems using the $0141 (eg, the "a <- line #, call $141, a == keys that are being pressed at line #" subroutine) subroutine. I noticed in the following program crashes after reading the keystrokes 4 or 5 times. I thought it might be the interrupt conflicting with my program in some way, but adding "di" didn't seem to help. Does anyone have any insight on this?

BTW, how can I access the keyboard directly, rather than going through the bios?


thanks for your time,

wur

-=============

db $fe
dw start
dw eof
dw exec

org $8800

start:

letter_a: db "You pressed 'a'. ", 0
letter_b: db "You pressed 'b'. ", 0
letter_c: db "You pressed 'c'. ", 0
exit_bye: db "x--Exiting, bye. ", 0

exec:

; disable interrupt

di


main_loop:

; scan line with 'b' / 'a', check for 'b' / 'a'

ld a, 2
call $0141
push af
and a, 10000000b
cp a, 0
jp z, &print_b
pop af
and a, 01000000b
jp z, &print_a



; scan lines with 'c' / 'x', check for 'c', then 'x'

ld a, 3
call $0141
and a, 00000001b
cp a, 0
jp z, &print_c

ld a, 5
call $0141
and a, 00100000b
cp a, 0
jp z, &quit_prog

jp &main_loop


print_a:

ld bc, &letter_a
call &puts

.wait:

; wait until the user lets go of 'a'
ld a, 2
call $0141
push af
and a, 01000000b
cp a, 0
jp z, &.wait

jp &main_loop


print_b:

ld bc, &letter_b
call puts

.wait:

ld a, 2
call $0141
push af
and a, 10000000b
cp a, 0
jp z, &.wait

jp &main_loop


print_c:

ld bc, &letter_c
call puts

.wait:

ld a, 3
call $0141
and a, 00000001b
cp a, 0
jp z, &.wait

jp &main_loop


quit_prog:

ld bc, &exit_bye
call puts
ei
.end: ret


puts:

ld a, (bc)
cp 0
ret z
call $a2
inc bc
jp puts
.end: ret

eof:

why the DI and EI ?
they don't help your conflict in no way. remove them, only brings more corruption.
Also you do a PUSH AF and after that a JUMP. This will corrupt the stack.
here for example:

Quote:

ld a, 2 call $0141 push af and a, 10000000b cp a, 0 jp z, &print_b pop af and a, 01000000b jp z, &print_a

when PUSHING a register you need to POP it, whenever, where ever.
a better solutions would be

ld a, 2
call $0141
bit 7,a ;check for bit 7
jp z, &print_b
bit 6,a ;check for bit 6
jp z, &print_a

another thing:
when using a AND instruction to check value, you don't 'ave to use a CP (the AND already sets flags)
like this:

Quote:

and a, 10000000b cp a, 0 jp z, &print_b

just use

and 10000000b
jp z,label

http://map.tni.nl/articles/keymatrix.php

read this article as well.
easy reading the keyboard like this:

keys: EQU #FBE5

;
;Check whether space is pressed
;
loop
ld a,(keys+8) ;space
bit 0,a
jp nz,loop

...

ret

the above works only when INTS are on (and the BIOS is used, unless you've got your own matrixscanner on the INT)

Here is BIOS independent version:

;
;Check whether space is pressed
;
in a,(#aa)
and #f0
or 8
out (#aa),a
loop:
in a,(#a9) ;space
rrca
jr c,loop

which answers wur's queston "BTW, how can I access the keyboard directly, rather than going through the bios?"