Date   : Wed, 04 Jul 2007 08:40:52 -0500
From   : julesrichardsonuk@... (Jules Richardson)
Subject: Anyone recognise these boxes on eBay?

Andrew Hancock wrote:
> So I assume, it connects to a rom socket eventually in the beeb!

Nope, directly intercepts the CPU bus - there's no connection at all to the 
internal ROM banks, just the CPU connection and a pair of wires running to S21 
on the beeb.

 From the manual diagram, it looks like ROMs #0-3 stay in the beeb, then 
within the external box slot #4 can be either a ROM or four mappable RAM ICs, 
and slots #5 to #14 can be ROM only.

The external PSU needs to be +5V (regulated I assume!).

The comms board internal to the beeb looks to just contain a pair of LS244 
chips, an LS245, and an LS126 (plus the 6502 CPU), so it doesn't look to be 
that complex for someone who has the right PCB-making stuff.

There's some surplus external ROM boxes at Bletchley, but I'm not entirely 
sure where they are right now (and I know there's no spare comms boards or 
power supplies - i.e. same deal as the ones in this ebay ad)