Sinclair ZX80 / ZX81 Forums

[siggi]

Do you know the C-compiler Z88DK? So you could write games also in C.

It supports also the ZX81 (e. g. true HIRES (Wilf Rigter) and moving sprites) and a demo game shows how.

See
http://www.z88dk.org/wiki/doku.php/

and

http://www.z88dk.org/forum/forums.php


Siggi

[XavSnap]

Can't download EO !!!
The file must be trunkated...

[sirmorris]

http://www.rwapservices.co.uk/ZX80_ZX81/forums/viewtopic.php?f=4&t=67&p=461

This might be useful. It shows a cheeky technique for liberating the IY register for use in slow mode.

Let me know if I can be of any further help.

-Charlie

[Moggy]

Sir Morris
do us a favour put the soldering iron and vero board away and get coding again!!!
I thought Andre had some off-the-wall games ideas, this ones a little cracker (sprites on a zeddy yeees!!!)
You've done in m/l what he does in basic 10 out of 10.

Regards Moggy

[BrunoFlorindo]

Nice to see Bob here! Maybe some of the current Speccy titles can have a ZX81 port? Ever since Mike Wynne was able to come up with a Speccy emulator for the Zeddy, I started to believe anything is possible!

And at some point, if possible, the new games could have optional AY sound. Not everyone has AY interfaces, but emulators would allow us to enjoy it.

[bobs]

Nice to see Bob here! Maybe some of the current Speccy titles can have a ZX81 port?

Just getting something on-screen in assembler will be nice to begin with! Once I've got into my stride though anything could happen.

[Colin]

Hi Bob,


I've just started playing with assembly language on an (emulated) ZX81. On a machine with an expanded display file (that is, on a machine with > 3KB RAM), the main thing to know is that there *must* be 25 Newline characters otherwise the machine will crash (or at least the display will become completely messed up).

The beginning of the display file is pointed to by the 16-bit value held at 16396 and 16397.

The first character must be a ZX81 newline character (decimal 118), this is followed by 32 display characters and then the line is terminated with another newline character. Each of the following lines is terminated by a newline character. Do not overwrite these characters by mistake!

I wrote the following routine for writing to the screen. You call MAKE_TABLE once at the beginning of your program, and then call PRINT_CHAR with a line, column and character value each time you want to put a character on screen. It uses a lookup table to hold the location of the first character of each line, and then adds the column position to get to the screen location.

I assemble this into a BIN file using the Pasmo assembler, then use a utility called BIN2P to transform that into a .P file with a BASIC loader ready to use in an emulator. (These tools are available for Linux, others will probably be able to advise what's best under Windows).

I'm very much a beginner at assembly language, so forgive anything that isn't clear or is suboptimal. The code is here, everyone please feel free to use it as you like:

Code: Select all

; Print Character Routine
;
; Prints a character at a
; specified print position.
;

;
; Entry point to print the character
;
; Registers:
; A   ->   Line
; B   ->   Column
; C   ->   Character to Print

PRINT_CHAR   LD   D, 00         ; Zero high byte of line counter

      ADD   A, A         ; Multiply line offset by two (2 bytes per line address)
      LD   E, A

      LD   HL, ADDRESS_TABLE   ; Point to beginning of screen address table
      ADD   HL, DE         ; Move pointer to address of beginning of screen line
      LD   E, (HL)         ; Store low byte of screen address
      INC   HL
      LD   D, (HL)         ; Store high byte of screen address
      EX   DE, HL         ; Place screen address into HL
      
      LD   D, 0            ; Put column position
      LD   E, B            ; into DE.
      ADD   HL, DE         ; Point HL to character position on line
      LD   (HL), C         ; Put character into display file
      RET

;      
; This routine only needs to be called once to create the screen line address table
;
MAKE_TABLE   LD   HL, ADDRESS_TABLE   ; Address table pointer
      LD   DE, (16396)      ; D_FILE
      INC   DE         ; Step over first control character
      LD   B, 24         ; Count 24 lines
TABLE_LOOP   LD   (HL), E         ; Store address of
      INC   HL         ; first character
      LD   (HL), D         ; of each screen line.
      INC   HL
      PUSH   BC
      LD   BC, 33         ; Add 33 characters
      EX   DE, HL         ; to screen address pointer
      ADD   HL, BC         ; (32 visible characters
      EX   DE, HL         ; plus newline)
      POP   BC
      DJNZ   TABLE_LOOP      ; Loop to process next line
      RET

ADDRESS_TABLE   DS   48         ; Reserve space for the 24 line addresses



Cheers,

Colin.

[thewiz]

Having read Colins message, I thought I would add how I handle screen address calculation. It might be a byte or two longer but doesn't need the table and takes the same amount of time regardless of coordinates. As I don't use basic once my M/c starts, the start of the display never moves so don't need to use (D_FILE).

Code: Select all

CALC    ld b, (xcoord) ; normally for player
        ld c, (ycord) ; normally for player
CALC0   ld h,0
        ld l,b
        push hl
        add hl,hl  ; x2
        add hl,hl  ; x4
        add hl,hl  ; x8
        add hl,hl  ; x16
        add hl,hl  ; x32
        pop de
        add hl,de ; x33
        ld e,c
        add hl,de
        ld de, <address of display + 1>
        add hl,de
        ld a,(hl) ; optional
        ret


I use the CALC0 entry point when b and c are set for another object, e.g. the enemy.

Enjoy