Sinclair ZX80 / ZX81 / Z88 Forums

On a real ZX81/TS1000, to get UDG, you need a memory chip to supply different data compared with the data in the BASIC ROM chip. Until the ZXpand and Andy’s UDG board, the only way (*) was to buy/make an internal ROM/RAM board and fit it in place of the BASIC ROM. They could have the BASIC ROM, a custom ROM, and a SRAM chip.

You could fill the SRAM chip with whatever character set you liked. But while this set is in use, the character set in ROM is not available, that is, you can’t mix and match. But you can copy the character data from the BASIC ROM.

(*) not including high resolution graphics systems and techniques.

Mark

My ideal would be a software only solution. Looks like WRX maybe the closest path there (?)....

If you look at Nuclear Invaders by Kelly Murta, he has made a game in Forth with UDG. After that he has made a WRX version with a few extra routines, that simulate UDG in WRX mode. The Forth source is included with the program, however the UDG-to-WRX routines you have to decompile yourself.

mrtinb wrote: ↑Mon May 03, 2021 9:00 pm If you look at Nuclear Invaders by Kelly Murta, he has made a game in Forth with UDG. After that he has made a WRX version with a few extra routines, that simulate UDG in WRX mode. The Forth source is included with the program, however the UDG-to-WRX routines you have to decompile yourself.

I made an UDG-routine for my SHOGUN game and that routine was converted to the USCII-routine so it was possible to use UDG in BASIC.

You always have the Pseudo High Res Graphics alternative which doesn't require hardware mods, it's a software only solution.

Thanks.

zx81ultra wrote: ↑Fri May 07, 2021 11:24 pm You always have the Pseudo High Res Graphics alternative which doesn't require hardware mods, it's a software only solution.

But there is no easy way to use it from Basic, like the great USCII-routine. And you can’t use the ZX81 charset, unless you use the same “I”-value as the ROM does.

However it would be possible to make a routine, like USCII, where you can display the normal characters, and custom characters where the 8 patterns for the char is taken from 8 different characters. Then some funny characters can be made, but they will be somewhat limited.

To make it even more flexible you can use the source from Paul Farrow’s Celebration Demo. With that routine you can change the “I”-value for each scan line on the screen.

I have no interest doing anything in basic. I'll check out Pauls stuff. I'm really looking to just remap a couple characters for use from assembly replacing a few of the stock characters - or replacing all of them if that's easier.

• Use dr. Beep's USCII if you want to code for WRX (needs WRX enabled RAM), or
• Use Paul's code if you need to run with PSG (Pseudo Hires Graphics) on unmodified hardware.

USCII will be easier, but Paul's code will work on unmodified hardware.

Spinnetti wrote: ↑Sat May 08, 2021 3:38 pm I have no interest doing anything in basic. I'll check out Pauls stuff. I'm really looking to just remap a couple characters for use from assembly replacing a few of the stock characters - or replacing all of them if that's easier.

See my SHOGUN in hires. It uses WRX-graphics and text all addressed with a chr.
CHR up to 191 are printed as normal or inverted, above 191 are user graphics. The same routine is used in USCII.