Sinclair ZX80 / ZX81 / Z88 Forums

Well - it might be useful for developers.
I am always thinking of which addresses have been in use by what modules and which one to take for new developments to avoid collisions. As in tradition to Sinclair most interfaces and modules are not fully decoded. This gives a quite fast overview and technical details to different modules known and widely used.

If I may have forgotten something (I guess there is much more hardware out ...) or made mistakes, any hints for updates and corrections and adding of more hardware modules is appreciated. As long as you can give as many details as possible. So I will update it regularly.

Have fun.

Hi Karl.

ZXpand+ also uses $07.RW, and port $17.R for a status bit.
It fully decodes $0f,$1f,$cf and $df for AY & on-board turbo-ay.

C

And if an AY module is attached, does it use standard (or which) ports additionally ?
I am a bit confused about usage of $CF/$0F and $DF/$1F.
Didn't found too much documentation of it.

As far as standard is concerned, one version of the Zon-x manual states DF and 0F are the register select and data registers respectively. In practice the decoding is so loose you could use any one of about 8 ports, but that's another story. I don't know where the CF register comes from historically.

ZXpand will address a single AY chip at any valid combination of register and data ports. So DF & 0F, CF & 0F, DF & 1F or CF & 1F. If a turbo board is fitted then CF & 0F are chip 1, DF & 1F are chip 2. A4 is used to discriminate in this case.

There are no other registers involved.

My earlier attempt at collating ZX81 IO port information is here

Mark

Thanks. Didn't know about your previous work (even if responded earlier but 5 years ago is much time). Jesus - is it 5 years now working on and with Sinclair Hardware ???

I think it is important to have the decoded bits to see, not just the main used address in software. It is complicate if hardware respond to other addresses as well. And a PDF format would be better as the XLS is opened on my Mac with another viewer who automatically converts all data (dec, hex, bin) into the decimal format.
I think it would be better to have a view from an interface side as it is more helpful to see what interface exactly conflicts and if it is an important one (widely used like ZXpand) and how to avoid best. On the other hand the list you created earlier is hard to follow as there is a PIO port named for example but don't know which module is meaned here. Which module is using SIO ports this way or CTC ? That is unclear for me.

So I think starting new now would be better. A bit difficult is the sorting criteria but I used here the main io addresses used.
I tried to put it all in detail as much as possible to get a good overview.
So at the end I hope this new list will help people here.

By the way - will wait about one week to update the list to let it all do in one tun - maybe there are more missing modules. So time to report here now.