DKtronics graphics ROM in ZXpand.

[Moggy]

I obviously didn't make my post clear enough.

I'm not referring to ROMS being REPLACED in the Xpand I'm saying that certain ROM images from various pieces of hardware can stored in the Xpand at the memory location occupied by real hardware and run as if the xpand was that hardware.
No dismantling-soldering-ROM replacing etc.

I never said it can do UDG only that certain parts of the DK'tronics ROM code concerned with character sets will run from the xpand which it does quite happily as does the ROM image from the Memotech Z80 assembler unit-memocalc-memotext (though some of these units have a physical switch making them not really viable but run none the less) , an EPROM based toolkit I have and one or two other bits I have with no disabling of the xpand ROM or any other ROM for that matter needed.

I just thought it an interesting observation nothing more and have no idea how Eighty One came into the discussion. .

[PokeMon]

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.

Can you explicitly state if ZXpand is showing the UDG chars on screen when loading this rom by "software" (no manual replacement inside) ?

There are ways by the way to create UDG's externally, most likely by presenting an own video output like ZX Chroma does. But it is not a simple step due to the internal resistors in a ZX81 (which are not emulated in most emulators but allow easy replacement of the starting ROM). It is easy to switch off the ROM and load another one but it is not easy to feed the ULA with corresponding graphic data during refresh cycle.

[Andy Rea]

I was be highly surprised if you can get true UDG from a zxpand without additional hardware, as a proof of concept i created a board that plugged in between zeddy and zxpand to create the alternate address lines in the 8 to 16k region thus allowing true UDG

Regards andy

[1024MAK]

Do you want a shovel, Moggy?

Mark

[1024MAK]

I think things have got a bit confused with this thread

What Moggy is trying to say, is that using the SRAM of the ZXpand mapped to the address area used by some of these add-ons and interfaces for their ROM chips, you can run the machine code that is in their ROM chips from the ZXpand SRAM okay.

What you can't do, is to have the dk'tronics (or other make/design) "UDG" (be it RAM or ROM based) work with just the ZXpand.

Mark

[gammaray]

This horse is not quite dead yet.

What you can't do, is to have the dk'tronics (or other make/design) "UDG" (be it RAM or ROM based) work with just the ZXpand.

Hires techniques notwithstanding, this is because the ULA character generation is limited to the block character maps at address $2000 1E00h-1FFFh ? that have to be internal hardware onboard for those particular maps to be utilized?

The dktronics ROM is not programs but the character maps?

I looked at the design and it appears that the ROM is 2K. What I have not figured out is the POKES that determine the memory range used...new thread?

[1024MAK]

The ZX81 is unable to use the normal display mechanism (BASIC ROM code, Z80 CPU and ULA) to create normal "lo-res" character data from anything other than the on board BASIC ROM. This is due to the "isolation" resistors that separate different parts of the internal bus. The connections on the edge connector are on the CPU side of these resistors (the wrong side).

The dk'tronics and similar "UDG" ROMs do contain some machine code to allow easy switching between different character sets.
However, I can't think of any practical use for this...

Moggy also talks about other ROM based expansions where the machine code also works from the ZXpand SRAM.

Mark

[PokeMon]

Mark is right - if you read the documentation of DKtronics board you have to replace the internal ROM or alternatively to pack (solder) the charset ROM on the back of the internal soldered ROM with some minor additional modifications.

I think it is possible to do an external UDG while providing an external scanline counter (A0-A2) and feeding the character code to the databus during refresh cycle (from an external charset ROM) and switching of the internal ROM through pulling /ROMCS high. The ZXblast was not developed to offer such feature and I think ZXpand either. But never give up hope for the future.

It is more easy to use high resolution graphics for this purpose.

[Moggy]

Do you want a shovel, Moggy?

Mark

Only to bury the blind buggers who, unlike your good self, seem incapable of understanding a simple post.

I WILL SAY IT ONCE MORE IN LARGE LETTERS, AS MY PREVIOUS POST SEEMS TO HAVE BEEN TOTALLY IGNORED, JUST SO IT SINKS IN.

I HAVE NOT AND HAVE NEVER STATED THAT THE XPAND CAN PRODUCE USER DESIGNED GRAPHICS OF ANY F***ING KIND WHAT SO EVER AND ONLY REFER TO EIGHTY ONE IN REGARD TO ITS MMC CARD FOLDER NOTHING MORE.

I ONLY, REPEAT, ONLY SAID THAT CERTAIN PIECES OF HARDWARE COULD HAVE ITS ROM CODE DUMPED INTO THE XPAND AND RUN LIKE THE REAL THING JUST FOR A BIT OF FUN, I NOW WISH I HADN'T BOTHERED!

SO THE ONLY THING I NEED TO "EXPLICITLY STATE" IS WHAT I HAVE DONE SO ALREADY IN PREVIOUS POSTS.

ALL CLEAR NOW?
CONSIDER ME DONE WITH THIS.

[gammaray]

We understood , some of us just got off topic and hijacked the thread... sorry