A0-A7 are at the same place. But both (ZX81 or SPECTRUM) use this memory segment for the SYSTEM ROM.
You can use a ZX81 card on a SPECTRUM only for IORQ resquest (IN & OUT process: sound cards, Input/Output, 8255, printer).
If you had to use a ROM or RAM on a SPECTRUM 16k, you had to use an edge connector converter (SPECTRUM>ZX81 or ZX>SPECTRUM).
The SPECTRUM use power pin on Z80 registers (/RESET, A10...)
You had to double check the card compatibility if you had to insert a ZX81/TIMEX 1000/TIMEX1500 or a TIMEX2068 on the SPECTRUM edge connector.
For those that want a searchable file, here is a text version manually transcribed from the PDF version of the user's manual at archive.org. I did proof-read it but didn't double-check everything
Weird... I guess archive.org doesn't list txt files alongside the PDFs? Look at the panel on the right: under Download Options you'll see there are 2 text files. One is your work.
It doesn't make any sense to turn this file (and the other text file, keys.txt) into PDFs. Maybe I'll ping the archive team to see what they suggest.
I've added a note to the page on my site about the manual; it'll show up in a couple of days when I run an export of the site and upload it to my server.
PS. Thank you! I never imagined the site and my collection would be so useful. I just wanted to preserve our history. I love seeing your posts as you go through the archive.
