9 Dec
2013
9 Dec
'13
11:14 a.m.
I've got a PDP-8A w/32K of core memory that I'm bringing up. For quite a
while I couldn't examine/deposit to anything but field 0 using the
programmers console. Pressing "000X" LXA never changed the field digit.
But by accident I tried doing an LXA with "3333" as the operand and it
started using field 3!. A little experimentation revealed that LXA was
using the tens (eights?) digit to set the address.
Now this PDP-8A is a 620 which means it really has the PDP-8E board set.
From reading the 8E maint manual when a load field is done on that machine
bits 6-8 of the switch register set the instruction field and 9-11 set the
data field. But the 8A user manual says that entering "0003" LXA should
work.
So it would seem that the 8A programmers console or the M8316 module needs
to replicate the lowest digit of the value entered into the tens digit to
work correctly. I can't see where that is done from looking at the
description or schematic.
Can anyone with an 8A programmers console verfiy that just entering "000X"
LXA sets the address to XYYYY (where YYYY was set with the LA button)?
Thanks,
Marc