This is a replica of the Control Universal board, the layout is as close as possible to the original although I only had photos of the top side to work from.
It is a very flexible board that can be loaded with 2 banks of RAM or EPROM usually 8K each but they can in theory be up to 32K. The RAM can be non-volatile if the onboard rechargeable battery is fitted.
The only modification made is that I have added an optional switch that can swap the two banks over. This allows for example an OS EPROM in one bank to be copied to RAM in the other bank and then swapped so that the RAM copy is active, memory locations can then be changed on the fly. I have used this to try out changes to VDU register values without having to keep reprograming EPROMs.
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The links and switches have the following functions:
LK1,2 - configure the memory banks
LK3,4 - these are a set of normally linked pads to which an optional toggle switch (DPDT) can be wired to enable bank swapping
LKA0 to 3-20/22 - bank A configuration links
LKB0 to 3-20/22 - bank B configuration links
SW1,2 - selects the 8K blocks for each bank of memory
SW3 - enables write protect on a RAM bank
Refer to the original schematic for details of the various configuration link settings.
64K RAM Modification
As standard the board is only capable of taking 8 x 2K RAM chips so 16K total even though the sockets are 28-pin so can accept an 8K 6264 RAM. However with a bit of modification the board can be configured to provide up to 64K RAM as follows:
Cut the track connecting pin 27 to 0V on IC's 8,9,10,12,13,14 (IC11 and 15 are OK)
Add a link from NWDS on Bank A pin 15 to pin 27 of IC's 8,9,10 (WE)
Add a link from NWDS on Bank B pin 15 to pin 27 of IC's 12,13,14 (WE)
Fit the Bank links as shown for '2764 MOSTEK' in the original schematic i.e. link 1-16, 4-14, 5-13, 6-12, 7-11 and 8-10
Fit the Pin 20/22 links crossed i.e. as shown for the 6116 in the original schematic (pin 20 CS1 connects to CE, pin 22 OE connects to 0V)
Fit links LK3 and LK4
I have permanently configured my board for use with Flex which can use 56K from 0000 to EFFF, so IC12 is not fitted and I have linked the Bank switches for 0,2,4,6 and Bank B for 8,A,C
Photo to follow
Schematic
Bill Of Materials
Front Panel Drilling
Blank PCB
