Date   : Sun, 27 Apr 2008 11:38:21 +0100
From   : ken.lowe@... (Ken Lowe)
Subject: Reviving a dead BBC+

Chris Thornley wrote:

> Do you have a schematic / Block Diagram showing how you have contented
> things together?

First attempt at making a schematic...
http://i300.photobucket.com/albums/nn18/chaser2001a/BBCPLUS128K/BBCPLUS64KExpansionSchematic.jpg
http://i300.photobucket.com/albums/nn18/chaser2001a/BBCPLUS128K/BBCPLUS64KExpansionBoardLayout.jpg

> I am presuming the two RAM chips are both are in parallel
> and the chip select line is used as an address line for the second chip?

Yes. /CS of both RAM chips is wired out to pins 8 & 15 of IC46 on the BBC+, 
which is an address decoder IC used to switch in sideways ROM / RAM banks. 
Pin 8 selects bank 12 / 13 and pin 15 selects bank 0/1. If jumper S13 is in 
the north position (which puts BASIC into bank 0/1) then it would be 
necessary to wire /CS to pin 7 of IC46 instead of pin 15 to pick up banks 
14/15.

> What does the ARM 1.12 ROM do? Rom 07?

Advanced ROM Manager is a useful utility for browsing and editing memory, 
including sideways RAM banks. It also allows you to load ROMS into sideways 
RAM banks - although the SRAM utilities of DFS1770 2.22 also allow you to do 
this. I'm sure there are plenty of other ROMS that do the same thing.

Ken.