Moving a Character in Machine Code

EgoTrip · 15:41, 08 December 10

This is really stupid, I have done it before but cant seem to get it working any more.

All I want is to move a character (for arguments sake lets say a star, char 42) with the cursor keys around the screen in 8x8 blocks, using the firmware, and I cant seem to get something this simple working.

Help please!

arnoldemu · 15:46, 08 December 10

Quote from: EgoTrip on 15:41, 08 December 10
This is really stupid, I have done it before but cant seem to get it working any more.

All I want is to move a character (for arguments sake lets say a star, char 42) with the cursor keys around the screen in 8x8 blocks, using the firmware, and I cant seem to get something this simple working.

Help please!

txt set cursor for positioning and txt output for drawing should do it for the drawing part, remembering to draw space where the old position was.

then you could use km read char for reading the keys, or km test key.

I have made some example code that moves a sprite around and that uses firmware for checking keys.

http://www.cpctech.org.uk/source/shftspr.html

this may help?

EgoTrip · 15:55, 08 December 10

I have already done what you suggested, it just doesn't work though, maybe I am missing something obvious.

What is the difference between read char and test key? I know one reads the char number and one the state of the key pressed, is that all or is there anything else? I used the test key in my attempt.

Edit: I would also like to add this is in Mode 1

EgoTrip · 16:02, 08 December 10

Actually sorry about all this, I just figured out what was wrong and it is all working now. All I needed to do was add in some PUSH AF and POP AF instructions.

Thanks for the help anyway!

EgoTrip · 16:13, 08 December 10

OK so its not working. After a while it crashes the computer.

Heres the code I have so far, yes its bloated and could be a lot better but I'm a novice.

Code Select


org &3000


call init


.mainloop
call keys
jp mainloop


.keys
ld a,0
call &bb1e
jp nz,moveup
ld a,72
call &bb1e
jp nz,moveup
ld a,2
call &bb1e
jp nz,movedn
ld a,73
call &bb1e
jp nz,movedn
ld a,8
call &bb1e
jp nz,movelf
ld a,74
call &bb1e
jp nz,movelf
ld a,1
call &bb1e
jp nz,movert
ld a,75
call &bb1e
jp nz,movert
ld a,47
call &bb1e
jp nz,fire
ld a,76
call &bb1e
jp nz,fire
ld a,66
call &bb1e
jp nz,quit
ret


.moveup
ld a,(ypos)
cp 1
ret z
push af
call prblank
pop af
dec a
ld (ypos),a
call prchar
jp mainloop


.movedn
ld a,(ypos)
cp 25
ret z
push af
call prblank
pop af
inc a
ld (ypos),a
call prchar
jp mainloop


.movelf
ld a,(xpos)
cp 1
ret z
push af
call prblank
pop af
dec a
ld (xpos),a
call prchar
jp mainloop


.movert
ld a,(xpos)
cp 40
ret z
push af
call prblank
pop af
inc a
ld (xpos),a
call prchar
jp mainloop


.fire
ld a,7
call &bb5a
jp mainloop


.quit
pop af
ret


.prblank
ld a,(xpos)
ld h,a
ld a,(ypos)
ld l,a
call &bb75
ld a,32
call &bb5d
call &bd19
ret


.prchar
ld a,(xpos)
ld h,a
ld a,(ypos)
ld l,a
call &bb75
ld a,42
call &bb5d
call &bd19
ret


.xpos db 10
.ypos db 10


.init
ld a,10
ld (xpos),a
ld (ypos),a
ret

arnoldemu · 16:37, 08 December 10

Quote from: EgoTrip on 16:13, 08 December 10
OK so its not working. After a while it crashes the computer.

Heres the code I have so far, yes its bloated and could be a lot better but I'm a novice.

Code Select Expand
org &3000 call init .mainloop call keys jp mainloop .keys ld a,0 call &bb1e jp nz,moveup ld a,72 call &bb1e jp nz,moveup ld a,2 call &bb1e jp nz,movedn ld a,73 call &bb1e jp nz,movedn ld a,8 call &bb1e jp nz,movelf ld a,74 call &bb1e jp nz,movelf ld a,1 call &bb1e jp nz,movert ld a,75 call &bb1e jp nz,movert ld a,47 call &bb1e jp nz,fire ld a,76 call &bb1e jp nz,fire ld a,66 call &bb1e jp nz,quit ret .moveup ld a,(ypos) cp 1 ret z push af call prblank pop af dec a ld (ypos),a call prchar jp mainloop .movedn ld a,(ypos) cp 25 ret z push af call prblank pop af inc a ld (ypos),a call prchar jp mainloop .movelf ld a,(xpos) cp 1 ret z push af call prblank pop af dec a ld (xpos),a call prchar jp mainloop .movert ld a,(xpos) cp 40 ret z push af call prblank pop af inc a ld (xpos),a call prchar jp mainloop .fire ld a,7 call &bb5a jp mainloop .quit pop af ret .prblank ld a,(xpos) ld h,a ld a,(ypos) ld l,a call &bb75 ld a,32 call &bb5d call &bd19 ret .prchar ld a,(xpos) ld h,a ld a,(ypos) ld l,a call &bb75 ld a,42 call &bb5d call &bd19 ret .xpos db 10 .ypos db 10 .init ld a,10 ld (xpos),a ld (ypos),a ret

your jp mainloop is the main problem. the call keys is pushing return address onto the stack, then after you process a key, you do something and then jp mainloop back. You should be using ret here so it returns back ok.

replace all the jp mainloop in your key functions and then you should be ok.

arnoldemu · 16:57, 08 December 10

Quote from: EgoTrip on 15:55, 08 December 10
I have already done what you suggested, it just doesn't work though, maybe I am missing something obvious.

What is the difference between read char and test key? I know one reads the char number and one the state of the key pressed, is that all or is there anything else? I used the test key in my attempt.

Edit: I would also like to add this is in Mode 1

read char translates the key and gives you a character that it pressed.
test key returns the key number.
I think read char is also dependant on the key repeat.
so you've chosen the best one.

EgoTrip · 17:20, 08 December 10

Thanks alot for your help

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Moving a Character in Machine Code