ZX81 and 6116

From: Glen Goodwin <acme_ent_at_bellsouth.net>
Date: Thu Mar 28 23:33:00 2002

> From: Tony Duell <ard_at_p850ug1.demon.co.uk>

> > The text refers to 2x2114 or a 4118 installed in the UK version and a
> > 2K option for export - possibly there are 2 versions of the board?
>
> OK, I've pulled my ZX81 apart. The PCB claims to be 'Issue 1'.

I have never seen any board marked "Issue 2." Did it exist?
 
> So, fit L2 if you install a 6116 (A10 on pin 19). Fit L1 if you install a

> 4118 (I am not sure what pin 19 is, I can't find a 4118 data sheet, but
> at least one schematic I have calls it 'E', presumably an active high
> enable signal). Fit either or no links if you install 2 * 2114s. Never
> fit both links, or you'll short A10 to the +5V rail.

Today I checked out about two dozen ZX81/TS1000s. They've been piling up
in a box and today I finally got to them. Here's what I found:

All of the 1K boards had two 2114s and no jumper installed.
All but one of the 2K boards had a single 2016 and L2 was installed.
One 2K board had a 6116 and L2 was installed. The board was operational
and appeared unmodified.
I replaced a socketed 2016 on a working board with the 6116 pulled from the
above-mentioned board,
and the board still worked.

So I think it's safe to say that L2 is required for a single-RAM-chip
board, and that a 6116 is a drop-in replacement for a 2016.

Never did see a 4118. Perhaps the use of it would change things,
jumper-wise.

Glen
0/0
Received on Thu Mar 28 2002 - 23:33:00 GMT