23 Sep
2008
23 Sep
'08
1:22 p.m.
On Tue, Sep 23, 2008 at 11:40:04AM -0700, Rick Bensene wrote:
A while back, I wrote a posting regarding RX01 OS/8
boot images for my
PDP 8/e. A lot of folks responded off-list with very helpful
information.
As it turns out, with the gracious help from everyone, I was able to
find some programs (dumprest) that did what I needed.
Excellent.
I know it's a shotgun
approach, but without an Omnibus extender, or a practical way to power
up the boardset outside of the 8/e, it seems the best way to go.
Do you have enough room in your machine to put the RK8E at the back
and at least poke at the front and back boards of the RK8E with
them mounted away from everything? It's not perfect, but it might
help get around a few obvious steps?
Also, I think it's Tony's technique, but you can solder jumper wires
to the RK8E boards and thread them out of the stack and monitor
signals that you normally couldn't get to.
Would it make sense to simply remove the 8881's,
and then put the
boardset in, and see if the machine behaves itself (since the bus is
actively pulled up by the Ombibus Load board) to get an idea of the
drivers might be bad (or logic that enables them is bad)?
Perhaps, but if you do that, do it one at a time so you have an
idea which one is pulling down the bus.
The problem is with parts. The RK8E uses SP380's
and 8253s' for bus
receivers, and 8881's for bus drivers. The 8881 are quad 2-input NAND
buffer/drivers, with open collector outputs. I've got a good number of
vintage TTL 7401 ICs which match pinout, and are open collector
devices, but I'm not sure if the 7401 will work as a replacement for the
8881, since I can't find data on the 8881 I don't know if they are
electrically compatible. I do have a few spare 8881s, but not enough to
replace all of the 8881's on the RK8E.
Was it 7401s that were individually qualified by DEC for a certain
current response, or was that 7438s?
I don't have any replacements
for the SP380s nor the 8253's, which seem to be rather unique, which
could be a problem. Anyone out there know if there are 7400-series TTL
replacements for these parts?
Please do check it, but ISTR the NS8640 is a valid sub for the SP380. Don't
know about the 8253s though.
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 23-Sep-2008 at 20:10 Z
South Pole Station
PSC 468 Box 400 Temp -70.4 F (-56.9 C) Windchill -104.8 F (-76.0 C)
APO AP 96598 Wind 9.6 kts Grid 25 Barometer 676.9 mb (10745 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html