Sinclair ZX80 / ZX81 / Z88 Forums

Hello All,
I've just got my ZX Interface 1 upgraded (thanks to Ian Gledhill at Mutant Caterpillar, who did an excellent job) to a cool running vLA1 and the version 2 ROM, and it works just fine on my Harlequin. However, it is not paging into my original ZX Spectrum 48k which is the computer I want to permanently
attach it to. I've done the PRINT p and RUN test as outlined by Brendan Alford's hardware manual, and my 48k is just not picking up the interface.

If I recall somewhere there was an issue with some Z80 CPU's not working with Interface 1: can anyone shed any light on whether this might be the problem?

Cheers,

Simon

Isn't this the problem with the broken M1 signal?

Hi Paul,

That rings a bell, and I know I have read about this somewhere, but Google has not been my friend so far to remind this!

At least Google "Z80 M1 interfaces" shows a number of results showing I was right.
And an entry show a post of me in a German Forum that exactly this happend to me.
Many years ago...

So, in that case I guess I have to swap out Z80s until I get one that works! Hope one of my spares does it! Annoyingly, I fitted a brand new IC into this Speccie to make sure it was reliable

You can get a working M1 line Z80 from here:

https://www.retroleum.co.uk/zx-spectrum-chips

Ironically, I think that is where the chip might have come from! Not to worry, I’ve got a boxful of Z80s, I’m sure I’ll find one. Just in case, is there anything else that could cause this issue? I’ve cleaned and re-tinned the edge connector, and I don’t think there is any solder splash or similar, but could anything else cause the issue?

UPDATE:

Okay, I now have Interface 1 working, and loading micro drives very happily..... BUT...

None of my modern Zilog Z80's would page ZX Interface 1, and the one that is working quite happily dates from 1986... And I tried 3 new Z80s!

Curious, as I thought the newer ones were supposed to be much more reliable.

I had a Spectrum+ that would not work with my DIVMMCFuture so replaced the Z80 with one from Retroleum and it was fine but I never tried it with a Microdrive.

Curiouser and curiouser….

So, after a bit of thinking on the responses to my post, I tried the new Z80s that did not detect the ZX interface 1 or microdrives, and therefore suspected of having a broken M1 line with another Spectrum. Again, no joy with Interface 1, but I tried my DivMMC Enjoy! as well, as I think this needs that all important M1. In all cases, it worked…

Err… should that happen?