Tandy T100 info

[Tony Duell]

> 
> 
> I just aquired a Tandy T100, really fun little machine.
> one of the first steps is to exten the ram (24k more is possible)

>From what I remember, the original RAM consisted of little ceramic 
substrates with 4 off 2K*8 static RAMs soldered to them. There were 
separate chip select pins for each RAM, all the address decoding was on 
the mainboard.

These modules were 0.7" (I think) wide. But it's possible, with a bit of 
careful bending, to get a normal 0.6" wide IC into the socket. You can 
put a nromal 8K*8 static RAM into the top 12 pins of each side of the 
socket (wiith pins 1,2,27,28 of the RAM haning off the end) and most of 
the signals match up. I did this in my Model 100. I then did some 
cut-n-jumper mods to get A11 and A12 straight off the address bus, to 
modify the address decoder appropriately (while still keeping the 
original 8K module in the lowest address possition), and to handle the 
power-down memory protection.

I should still have notes on this, but I was working on a UK model, which 
doesn't have the intenral modem, and where different sections of ICs are 
used in some positions (what I mean here, is that if the US schematic 
shows, say, U6a as a '00 NAND gate in some position in the circuit, then 
the UK version still uses a '00 NAND gate, but it might well be U21c (the 
component references are totally ficticious here!)).

-tony