Sinclair ZX80 / ZX81 / Z88 Forums

Don't know if this has been done before but thought I'd share anyway.

One of the nicer features of the Xpand is the ability to put code more or less anywhere in memory.
I have found from messing about in general that certain ROM images from peripherals can be loaded and run from the xpand like the real thing,provided no physical switching is required.(IE Memotech HI-RES pack)

one example being the ROM image from the Memotech Z80 assembler unit which can be run successfully from the xpand.

Today I have been playing around with DKtronics graphic ROM and although I have not gone deep into it I found it does load successfully and all the USR calls seem to work.

Just put ROM image called rom.rom,in the attached folder, onto the Xpands SD card or in the MMC folder if using Eighty One in xpand mode.

To load, type LOAD "ROM.ROM;8192" (making sure the xpand is set for ram in that region) then follow the instructions included in the attachment to this post, then have fun.

The ROM image and accompanying files I downloaded from Simon Holdsworths' most excellent site found here...

http://www.zx81stuff.org.uk/zx81/hardware/0


EDIT
Forgot to add ROM file, now added.

Isn't some hardware needed to create UDG?

mrtinb wrote:Isn't some hardware needed to create UDG?

More than likely it needs some static RAM, I note the board has one 6116 static RAM chip fitted, but it works for all the Chrs sets listed which is good enough for most uses and I may try loading the ROM to my 8k battery backed 6116 Static RAM board and see what happens although there appears to be no instruction on how to create UDGs apart from ordering some software from DK.

EDIT software found.

At first look it doesn't seem to work on ZXblast. I'll try again when I get an updated firmware.

EightyOne is not real hardware. You can easily replace ROMs which has to be replaced physically in a real ZX81. If you see the instructions, the ROM has to be changed internally. The reason is, that in char/text mode the charset is addressed through the ULA which uncoupled the ROM from the address bus using resistors. This can not work this way with external hardware like ZXblast or ZXpand.

PokeMon wrote:EightyOne is not real hardware. You can easily replace ROMs which has to be replaced physically in a real ZX81. If you see the instructions, the ROM has to be changed internally. The reason is, that in char/text mode the charset is addressed through the ULA which uncoupled the ROM from the address bus using resistors. This can not work this way with external hardware like ZXblast or ZXpand.

But above Moggy mentions nothing about EighthyOne. He talks about ZXpand.

Not sure but this early manual states explicitly, that UDG can not be supported by ZXpand due to hardware requirements. Not sure if there was ever a change.

http://www.rwapsoftware.co.uk/DOC/ZXpand%20Manual.pdf

regardless of the zxpand, there 'might' be a way of an external udg unit..wilf rigters chrsx16 replaces the character set externally, but with a 'fixed' eprom, i tried to work out how to mod this circuit so it uses a ram and can be programmed at will making fully programmable character sets, i never got round to building the thing to see if it would work, if i can find the circuit i'll post it somewhere here, if anyone would be interested???

wilf or someone else may have already done such a thing,..????

as for using this with a zxpand, could be problems as this needs to patch out the rom under refresh cycles, will need to mod the zxpand so its rom and the zx rom can be disabled...