9 Dec
2013
9 Dec
'13
5:51 p.m.
On 09/12/2013 19:14, Marc Howard wrote:
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.
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.
Because it doesn't :-)
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)?
I don't have an 8A right here right now, and it's a few weeks since I
last used one, but when I wanted to set the extended address with LXA
I'm sure I set it the same way as on an 8/E. That is, bits 6,7,8 set
the instruction field and bits 9,10,11( the rightmost) set the data
field. So it's doing exactly what it should.
The PDP-8/A Handbook agrees with me. Page 5-9:
LXA Depressing LXA (load extended address) loads the right most
digit of the entry into the data field (DF) register and
the next digit of the entry into the instruction field
(IF) register.
--
Pete Peter Turnbull
Network Manager
University of York