ZX-81 custom chip - watizit?

From: Hans Franke <franke_at_sbs.de>
Date: Fri Jul 31 10:13:26 1998

> I just got a ZX-81 kit (unassembled). I didn't know this before, but the ZX
> uses a custom 40-pin IC to perform certain I/O functions. Is this chip truly
> "custom" or is it a relabeled Z80 support chip?

Yes, it is. Or better it is a semi cusom chip - like ASICs today.
The Basic design is a standard compilation of TTL functions, only
the last metal layer is custom. This was an early attempt by some
chip manufacturers to cut design costs - only this last layer had
to be designed for every customer. The technic was(is) called ULA
Unassigned(?) Logic Array. And thats also the name used by ZX-fans
for this Chip.

The ULA replaces something like 15 or 20 standard TTL bugs from the
ZX-80 design - the 81 is just a ZX-80 II :)


P.S.: Don't assemble it ... I assembled 5 kits several years ago -
      and now I could cry for one :(

Ich denke, also bin ich, also gut
Received on Fri Jul 31 1998 - 10:13:26 BST

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