I beleive (although, like you I've not checked
because, also like
you, I have as little to do with Sinclair machines as possible)....
It's not that I don't appreciate the skilful design work which went into the
ZX-80/81/Spectrum (much of which seems to be cribbed from "The Cheap Video
Cookbook" BTW), it's just that the first machine I had at home was a ZX-80
and programming the thing was a nightmare.
You were constantly having to program "around the system" because of the
"tight" way the hardware and firmware were tied together. It really was a
never ending, uphill battle, to get the thing to do anything useful which
eventually just got plain annoying....
I've not actually touched a Sinclair machine since I got my first Atari in
1983; and I hope never to again.... ;-)
TTFN - Pete.