Date   : Tue, 26 Oct 2010 09:23:43 +0100
From   : pete@... (Pete Turnbull)
Subject: Reversing the Tube ULA (destructively)

Paul Asin wrote:

> One problem, there are actually 3 different versions of the TUBE
> chip. One is the original 6502 cheese wedge, one is for the
> 6502/80186 internal copros (pn: 2201,266),I forget what the 3rd one
> is.

The original Tube ULA was made by Ferranti (part no 201,605).  The 
second version is an AMD chip (2201,266) which isn't an exact 
replacement, nor is it pin-compatible.  It's a CMOS device and was 
introduced when Ferranti ULAs became unavailable (to Acorn; they still 
had spares), in 1987.  The third device is a daughterboard (0359,400) 
which has one of the AMD chips, three transistors, and about 10 
resistors, and is called the Bipolar Tube Emulator PCB.  It was used as 
a replacement for the Tube ULA in most wedge co-pros, notably where the 
co-pro would work on a Beeb but not on a Master 128, because it's timing 
is a little different.  However it wasn't recommended for use in ACWs, 
though I'm not sure why.  IIRC it had problems with 32016 co-pros (eg 
Master Scientific).

So if you're going to make a copy, I'd say copy the original ULA.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York