🚀 go-pugleaf

#R:ariel:-14600:uiucdcs:10500010:000:1319
uiucdcs!schwager    Dec  5 00:11:00 1982

If you dont mind going mailorder, try the back of Computer Electronics or
Radio-Electronics for ads of places selling ZX-81 stuff.  I have a 
catalog from Gladstone Electronics and they might have some books covering
some of the info you're looking for.  I know there are two volumes out
that give a complete disassembly of the 8k ROM: "zx81 ROM Disassembly, 
Part A" and "zx81 ROM Disassembly, Part B", by Dr. Logan (whoever he is).
Part A covers 000H to 0F54H (this excludes the floating point calculator).
Part B covers 0F55H to 1DFFH (includes all routines used in the floating
point calculator).  They have another book, "The Explorers Guide to the
zx81" that looks like it carries a lot of general info.  The description
says it covers programming aids for BASIC, some macihine language topics.
Also, "ROM routines, ROM tables, load & save instructions, display file info,
and keyboard scanning are all discussed in (sic) The Hardware Chapter gives
informationon how to connect an external keyboard, connecting a monitor, 
hooking up a speaker for listening while saving or loading, and gives 
circuit diagrams of 1-4k RAM, 24 line I/O, 16k RAM, and more."
Hopefully Santa Claus will bring me that book.  Send me some mail after
Christmas and maybe I will have some more detailed info for you.
Hope this helps.