why wont this code increase the number displayed on the screen each time?

[777]

Code: Select all

org 40000
call 3503
ld a,0
start
inc a
rst 16
jp start

i have no idea...

[PeterJ]

RST is printing the Character code @777. Look at page 135 onwards of the original Spectrum manual in the code column.
Try starting A at 48 which is a 0. After 9, you get the maths symbols then A-Z

[777]

sorry, i meant character.

nope, it still gets stuck on 9's...

[PeterJ]

sorry, i meant character

Yes, so set A to 48

[777]

tried that, it still gets stuck on 9's...

[PeterJ]

nope, it still gets stuck on 9's...

It will because after 9 comes the maths characters and A-Z

[Luzie]

Code: Select all

org 40000
call 3503
ld a,0
start
inc a
rst 16
jp start

i have no idea...

Fast idea: Try with PUSH before rst16 and POP after rst16:

Code: Select all

org 40000
call 3503
ld a,0
start
inc a
push af
rst 16
pop af
jp start

[777]

ok, i c. so i should use the calculator routine?

[jimmy]

...because RST 16 does the same as PRINT CHR$(A) in BASIC. It also destroys the value of A when it has finished.
If you want to print a number (0-9999) you can use another ROM routine:

Code: Select all

org 40000
call 3503	;ROM routine CLS
ld bc,0		;start counting from 0
loop:
push bc		;preserve BC as routine below destroys value
call 6683	;ROM routine OUT-NUM
pop bc		;restore BC
inc bc
jr loop

[777]

Fast idea: Try with PUSH before rst16 and POP after rst16:

yea that works, but that is weird cos i tried that before...

[Dr beep]

The RST 16 effects A, so PUSH Iand POP is needed.