Spectrum Computing

chilledgamer wrote: ↑Thu Jun 25, 2020 4:28 pm

R-Tape wrote: ↑Thu Jun 25, 2020 4:22 pm There are quite a few ROM disassemblies out there. Here's one (I put it on my own webspace. I think it's by Geoff Wearmouth, but I couldn't find his link. Am I allowed to do this?) If you search this text file for "0DAF" (3503 in hexadecimal), you'll see the CLS routine (or you can look at the memory address in your emulator debugger).

RST 16 is the same, it's listed under "0010" (16 in hex). 'RST' is basically a CALL, but faster because it has special wiring (that phrasing will drive the hardware nuts wild ). So CALL 16 will do exactly the same as RST 16, but ever so slightly slower (there will be no noticeable difference though).

My advice at this is it: DO NOT TRY TO UNRAVEL THESE ROM ROUTINES YET! They are a nightmare and if you're anything like me, you'll get tangled in confused, hateful knots in no time.

I'd just use them for now, understand that CLS clears the screen & sets paper colours, and RST 16 prints stuff. Even though the ROM code is a mile long, you can write your own CLS, PAPERFILL and PRINT routines in tens of bytes. We can post some if you like.

Though IMO, starting off just using the ROM routines without worrying too much about their contents is a good way to get into coding.

This is really helpful to me thanks!!!! Could I ask about RST 16 again. In the example (im sure your aware of it) he uses RST 16 to print, i get that no problem. But later he 'sets' the xy position of the character for player. After each set of accumulator, he does RST 16 with comment "set the player x coord". Nothing is printed with this action i assume?

code snippet:

Code: Select all

basexy 
	ld a,22 ; AT code.
	rst 16
	ld a,(plx) ; player vertical coord.
	rst 16 ; set vertical position of player.
	ld a,(ply) ; player's horizontal position.
	rst 16 ; set the horizontal coord.
	ret
; Show player at current print position.
splayr 
	ld a,69 ; cyan ink (5) on black paper (0),
; bright (64).
	ld (23695),a ; set our temporary screen colours.
	ld a,144 ; ASCII code for User Defined Graphic 'A'.
	rst 16 ; draw player.
	ret

chilledgamer wrote: ↑Thu Jun 25, 2020 4:28 pm This is really helpful to me thanks!!!! Could I ask about RST 16 again. In the example (im sure your aware of it) he uses RST 16 to print, i get that no problem. But later he 'sets' the xy position of the character for player. After each set of accumulator, he does RST 16 with comment "set the player x coord". Nothing is printed with this action i assume?

org 32768
	ld a,2
	call 5633
	ld a,32
loop:	push af
	rst 16
	pop af
	inc a
	cp 165
	jr c,loop
	ret

chilledgamer wrote: ↑Thu Jun 25, 2020 5:52 pm Thank you all. I wangled the night off work haha I understand much better now about RST , which has helped me somewhat understand the whole thing a little better also.

R-Tape wrote: ↑Thu Jun 25, 2020 8:51 pm

chilledgamer wrote: ↑Thu Jun 25, 2020 5:52 pm Thank you all. I wangled the night off work haha I understand much better now about RST , which has helped me somewhat understand the whole thing a little better also.

You have a very understanding boss!

Mr Pargeter? I'm afraid I can't come to work tonight; I need to unravel the convoluted wonders of the RST 16 instruction on the ZX Spectrum.

chilledgamer wrote: ↑Thu Jun 25, 2020 11:00 pm By the way, I think I might have found a mistake on Skoolkid site https://skoolkid.github.io/rom/maps/all.html , here he lists "2294 The Border Command Routine" but in my example tutorial and all of my testing I have to use 229B. Anyone see if this is the website that is wrong, or yet again me being dumb lol?

chilledgamer wrote: ↑Thu Jun 25, 2020 11:00 pm By the way, I think I might have found a mistake on Skoolkid site https://skoolkid.github.io/rom/maps/all.html , here he lists "2294 The Border Command Routine" but in my example tutorial and all of my testing I have to use 229B. Anyone see if this is the website that is wrong, or yet again me being dumb lol?

L2294:  CALL    L1E94           ; routine FIND-INT1
        CP      $08             ; must be in range 0 (black) to 7 (white)
        JR      NC,L2244        ; back to REPORT-K if not

229B       OUT     ($FE),A         ; outputting to port effects an immediate
                                ; change.