Sinclair ZX80 / ZX81 / Z88 Forums

Hi, Just an update on the vLA81 issue that I have been experiencing. Having followed all the suggestions offered to me, I eventually tried it in my other ZX81 with the same result. Charlie Ingley (the Creator of the vLA81 for those that don’t know) has been incredibly helpful, as have these forums u...

Ok, I will do what you suggest and check the board again for any solder splashes and do that sanity check. I have got another ZX81 which I can test the vLA81 in, I’ve just been a bit reluctant up till now because it’s all back together etc. It’s an internal 16K RAM with the standard ULA in so obviou...

Hi Mark, I have finally got the 32K RAM installed with a connection to pin 35 of the vLA81 and the Z80 address line successfully, with the help that you supplied! Ignoring memory mode 0, no matter how I set the USR0 / USR1 switches the memory mapping is always as shown in the images. I contacted Cha...

Hello everyone. I installed the full 32K on a ZX81 with a vLA81 successfully with a lot of help from Mark (MAK1024)! The connection to pin 35 on the vLA81 to enable the extended memory addressing has been made. (Z80 address line A13 and one of the SRAM address pins, in this case as it happens, addre...

I have now successfully installed the 32K memory using the vLA81. Thanks Mark. Understanding the memory mapping the ZX81 uses is also becoming a lot clearer (so I thought), thanks to the various posts pointed out to me, and others I have come across. I remember from day one reading how the ROM and R...

Hi, I now understand that with the SRAM it doesn’t matter in which order the address out lines connect to the Z80 address bus, so long as they do. I did not appreciate that, and it has cleared up a lot of confusion from things I have seen on-line. The first image is how I had it configured originall...

Hi Guys! Thanks for all you info so far. I am certainly enjoying my trip so far, wealth of info on ZX81 that I had no idea about. Certainly don't know how you find the time to deal with all this! Mark, you have already replied to my first (I know it won't be my last) post on this forum with very det...

Hi Mark

Just read your reply, thanks.
I'm going to fully digest that tomorrow now!

I'll let you know how I get on with it all.

Cheers

Mark

Ok!
Thanks for the re-assurances.

Maybe I should just un-bridge and try it again I guess.

Hi Moggy Thanks for the feed back. I have looked at the clip and I think that bridge shouldn't be there as well. I was just going to remove the bridge, but then I thought about what if I have to return it because it's faulty, opens up all sorts of potential hurdles with the supplier. As you know the...