4 Feb
2015
4 Feb
'15
6:53 p.m.
On 2015-Feb-04, at 6:10 PM, Pete Turnbull wrote:
On 04/02/2015 17:40, Noel Chiappa wrote:
This is all interesting, does anyone have a reference/source for the J11 part # suffix vs.
clock speed?
I was wondering about J11 clock speeds a few months ago, mostly out of curiousity, while
working on a little project,
(leaving aside clock speed, PDP11 geeks might find it mildly amusing):
http://www.cs.ubc.ca/~hilpert/e/pdp11hack/index.html
Notice the link in there to an article by Bob Supnik that refers to clock speeds down in
the 3-5 MHz range. I wonder what's going on there - if what Bob is saying is accurate
how did this chip design ever reach 15/18/20MHz?
The J11 I have has a suffix of -08, and 1987 date code.
So I've seen some references which say that
the M8190-AB and -AC
(w-o/w FPJ11 FPP chip) are 15 MHz "11/73" CPUs for QBUS use, and the
M8190-AD and -AE (w-o/w FPJ11) are 18 MHz "11/83-84" CPUs for UNIBUS
use (via the KTJ11-B convertor, of course). (Of course, the /83 is
nominally QBUS, but let's ignore that for the moment... :-)
However, I'm wondering if this is correct...
I have a CPU board out
of a 11/84 (one owned by DEC, no less!) which says M8190-AB on the
handles, but the clock crystal says "18.432", and it has a
57-19400-09 J11 chip, which seems to be the 18MHz version (the 15Mhz
seems to be -04).
There were various revisions of the J11 chip, which was originally
designed to run rather faster (more than 20MHz) than early ones were
found to be capable of reliably. So "slow" ones were clocked at 15MHz and sold
as 11/73 boards, faster ones clocked at 18MHz and sold as 11/83 (or later as /84 -
there's no difference at all in the boards). To further differentiate the two, DEC
arranged 11/83s with PMI memory, and 11/73s with normal QBus memory, but both boards are
capable of running in either memory configuration. Additionally, 11/83s normally had the
FPA as standard.