ZXpand with UDG Characters

[RWAP]

Now this is something I had not realised, and there are some users who are also confused about this, so I though it would be better to open a new topic.

The two UDG character set schemes used by some games cannot be implemented on the ZXpand per se, as they require a board which has to be fitted internally on the ZX81 - the board will have its own memory, taking the ZX81s internal memory over the standard 1K.

There are two UDG schemes which I know of:

• * User Defined Graphics Card located at 3000h
  * UDG chr$ 128 card located at 3000h.

The ZXpand CAN work with ZX81s which have these boards fitted, but requires some modification so that it does not page itself in over the top of the extra RAM. There is a minor modification to the hardware required and a new GAL - see viewtopic.php?t=504#p4283

If people want a modified ZXpand, then please let us know when ordering - or if you already have a ZXpand, it can either be returned for the modification, or we can supply the replacement GAL for a minimal charge.

[RWAP]

I wonder if there is enough call to offer a UDG board - it depends which of the various hi-res schemes, programmers prefer I guess.

Then again, is the information available to create a UDG board without infringing copyright, and which of the two UDG schemes should be provided?

[Andy Rea]

I reckon it's possible to build a single chip (small cpld) inline interface (fits between zeddy and ZXpand) that could allow the 8-16K (or part of') the zxpand memory to be used for UDG's.

Regards Andy

[sirmorris]

How would the data get to the other side of the resistors??? I thought the reason that UDG _has_ to be an internal mod is that the eddy can only access data on the ULA side of the resistor fence when generating display?

[Andy Rea]

ah ah... it's magic... (and it's teh address bus that the problem not the databus, databus is a problem when trying to force nops)

but really, it's possible to create a line counter (used for A0, A1, A2) at the expansion bus by counting the HALTS, each scan line is terminated by a HALT, the character data (d-file byte) can be latched on the rising edge of the /RD, and then you can selectivaley (a bit of clever logic) choose which set of address lines to use during the refresh.

it's not my genius (I'm not that clever !)

see here http://www.user.dccnet.com/wrigter/inde ... CHR$X4.htm

so with a bit of clever decoding (to select when the alternate address is used) you can practicaly use any address space for UDG's, i guess some way of choosing between UDG mode or normal (for hi-res) would be useful too.

Regards Andy

[sirmorris]

...!

Oh man - if only I'd read that a couple of years ago Seriously though, laying out the zxpand was hard enough without another 2 chips on there

What about I open up the design so ZXpand 2 can have chr$16? It'll need a cpld rather than the twin GALs, and although SMD memory would save space it'd be harder to lay out, so I'd prolly stick with dip...

I wonder if people are wondering what all the 'spare' component places are for (it's not UDG)

[RWAP]

If this could be implemented in some manner, that would be great - maybe a small board to go between the ZX81 and the ZXpand

[Andy Rea]

i'll knock something up in the next few weeks and see how we go...

Andy

[Andy Rea]

Further to my last post and the excitment of the weekend, i've been spurred on to actually work on a little something, i have something working, kind of and will post some pistures soon, but now i want to know where i can download some alternate character sets for the zeddy. it's a little tedious poking, 512 bytes by hand

or is there a UDG editor somehwere ?

Regards Andy

[Prime]

Further to my last post and the excitment of the weekend, i've been spurred on to actually work on a little something, i have something working, kind of and will post some pistures soon, but now i want to know where i can download some alternate character sets for the zeddy. it's a little tedious poking, 512 bytes by hand

What format do they need to be in ?

I guess 8 bytes per character 1bpp making a 8x8 grid ?

If so I may have a couple of fonts that you could try, one is extracted from the Dragon Alpha rom and the other from the Spectrum.

I can let you have them as an ascii table or could prolly compile them to binary....

I guess they'd need to be in ZX80/81 character order tho.

Cheers,

Phill.