below

On Fri, Oct 10, 2014 at 3:21 PM, Engel, Michael <M.Engel@leedsbeckett.ac.uk> wrote:

That's what I also thought. Do you know if there were systems which used
P2 to connect to memory boards?

Pretty much everyone that was successfull - Masscomp, Apollo, etc... And they are all different.

Luckily, the driver chip for the UART RX line is an AM26LS32. While
this chip is no longer available, I can get an AM26LS32A here at Farnell
(which is just around the corner from my house :-)). Does anyone know
the difference between the 26LS32 and the 26LS32A? I only found a
page at TI that didn't list specific differences...

Hmm...

I looked in my old AMD books, and I unfortunately do not have an AM26xxx anything in there.

the difference between the MC1489/SN75189 and MC1489A/

SN75189

is input hysteresis on the receiver side. I wonder if AMD did the same when they created the 26L32

to compete with Moto and TI (in those days the 1488/1489 system was king until MAX shows up on the scene with a single 5v device).

So, I'll give you the text from Page 5-42 of the Moto Interface book on the 1489/1489A:

The MC1489 input has typical turn-on voltage of 1.25 volts and turn off of 1.0 volt for an input hysteresis of 250mv. The MC1489A has a typical turn on a 1.95 volts and turn off of .8 volts for typically 1.15 volts of hysteresis.

I suspect the A version will work fine, usually the differences was things like this where they made the part better in real world applications (250mv of hysteresis for a device that was supposed to be able to handle swing between +30/-30 volts is tiny).

Best of luck.

Clem