Hi-res issues with ZXpand

[Moggy]

Just a very silly thought.

When I got my first Xpand a long while back I fitted it in a Memotech case as suggested.
My particular case had the Velcro strips fitted as did the 81, that Memotech supplied to hold case and computer together. The thickness of these strips cause the edge connector to stand off or not fully slide home to the 81.

Whilst in this configuration my display had a lot of the corruption that yours shows and the only way to stop this was to remove the Velcro and slide the Xpand further onto the edge connector.

Weird but just something to think about.

[britain4]

YUP

LOAD"25ANNI";X

Which loads file then disables the EPROM. A reset is needed to restore but I don't think that's the problem here.

Cheers. That has actually worked! Yay! I've just read it in the manual today so an important lesson here - RTFM!

This isn't something that bothers me as long as it's normal behaviour for the device - it's just weird it worked normally at first!

Thats a good suggestion as I had problems like that when I very first got it before I cleaned the edge connector. Soon as I did that, it worked fine ever since!

I'm now debating whether to mod the ZX81 for UDG (which will mean WRX will no longer work with the internal memory but presumably will with the ZXpand)

[sirmorris]

Great news

Just as a qualification of my question about the internal 16k expansion I'd like to say that if an internal RAM expansion doesn't disable itself when the ZXpand is connected then you'll have two RAM chips driving the bus. If the CS pin of your expansion uses the existing CS signal then everything should be OK. ZXpand jams 5 angry pixies onto the nRAMCS line at the edge connector, effectively disabling the internal RAM.

The last time I was on a bus that had 2 drivers ... well let's just say it didn't end well.

[1024MAK]

UDG means you need RAM mapped to the address lines of the ROM socket so that the ULA can control it. This is very different to the connections of the socket for the RAM chip on the board (which are on the CPU side of the address lines) with "isolating" resistors inbetween. This is the reason that you don't see UDG expansions that connect externally - it's not possible.

There is far more hi-res stuff than UDG stuff these days. If you did want UDG, you are better off using another SRAM chip on or under the existing ROM (or EPROM).

Now that I have a ROM board (see here and here), I intend to try UDG in RAM one day... but have not yet found time

Mark

[britain4]

Great news

Just as a qualification of my question about the internal 16k expansion I'd like to say that if an internal RAM expansion doesn't disable itself when the ZXpand is connected then you'll have two RAM chips driving the bus. If the CS pin of your expansion uses the existing CS signal then everything should be OK. ZXpand jams 5 angry pixies onto the nRAMCS line at the edge connector, effectively disabling the internal RAM.

The last time I was on a bus that had 2 drivers ... well let's just say it didn't end well.

Gotcha! Sounds like that could have gone badly then if I hadn't realised

UDG means you need RAM mapped to the address lines of the ROM socket so that the ULA can control it. This is very different to the connections of the socket for the RAM chip on the board (which are on the CPU side of the address lines) with "isolating" resistors inbetween. This is the reason that you don't see UDG expansions that connect externally - it's not possible.

There is far more hi-res stuff than UDG stuff these days. If you did want UDG, you are better off using another SRAM chip on or under the existing ROM (or EPROM).

Now that I have a ROM board (see here and here), I intend to try UDG in RAM one day... but have not yet found time

Mark

This is what I had gathered from reading up on it. I really just wanted to play Galaxians in hi-res! I'll look into the SRAM under the ROM chip version of the mod then - I thought if I could run WRX from the ZXpand and UDG from the internal memory it'd be a fair compromise but I'm going off that idea now... Seen a nice simple mod on here that's literally just connecting the address lines from the ROM to the RAM chip. I'll probably just leave it as it is.

[Moggy]

Couldn't resist.

Haven't tried it on real kit but it works well enough in SZ-81 emulator.

[mrtinb]

Couldn't resist.

Haven't tried it on real kit but it works well enough in SZ-81 emulator.

In VB81_XuR it is not the UDG-settting that needs to be enabled. It's the setting: Allow Writes to Shadow ROM (8-16K area).