ZX81 and 6116 - test-drb@ccmp.vtda.org

26 Mar 2002

...
  From: Tony Duell &lt;ard(a)p850ug1.demon.co.uk&gt;

I wrote:

...
  > After checking the schematic I find that there is
a link.  "Use L1 for 1K
...
  > RAM, use L2 for 2K RAM."  This tells me that
when a 4118 or two 2114s are
...
  > used (or a 6116???) there is no need to change
the jumper -- it's only
 > required when using a 2KB 2016 or equivalent. 
Tony replied:

...
  What is this link connected to? What does it
reconnect?  
Ok -- I have yet another version of the schematic here, and it agrees with
the first -- L1 for 1K and L2 for 2K but does NOT specify what this means
in terms of the actual number of RAM ICs onboard.

...
 From looking at the schematic from the ZX-TEAM web
site, I can't see how either jumper would affect a two-chip configuration.  L1
ties the single
RAM chip's A10 to +5V, while L2 ties the single chip's A10 to the A10 line
on the system bus.

Can you make any sense out of this, or is it necessary to be Clive Sinclair
in order to understand it?

As mentioned in a previous post, the 2-RAM-chip ZX81 PCBs I have at hand
have NEITHER L1 or L2 installed.

I would consider experimentally changing the links L1 and L2 and seeing if
this made a difference in the amount of RAM present, except that we're
talking about +5V and I don't want to toast any ICs, even common ones, if I
can avoid it.

Any insight you can provide will be helpful.

Glen
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