UNIBUS RAM with Parity vs. None

william degnan billdegnan at gmail.com
Fri Oct 9 12:24:23 CDT 2015

(cross posted to MARCH list)

Question about UNIBUS RAM with Parity vs. None

I assembled a pdp 11/05 in a BK11-K box with a sticky 5 light -  I can load
an address, but the 5 light will erroneously (often but not always) light
when I examine.  Once 5 is turned on it stays on, even if the toggle switch
is down.  Once this occurs I cannot deposit nor can I  examine contents of
RAM.  I intend to test the front panel to verify that toggle 5 is ok
electrically, this is a to-do.

The power checks out including DC LO AC LO.  I transplanted the CPU cards
into another system to test and they work also.  Aside from the console
itself, it must be a RAM problem.

The system has 8K Core
G235 (xy drive module)
H217D (memory stack)
G114 (sense / inhibit)
M8293 (memory control module)

My question - I have read, and to the best of my understanding believe I
can swap an H217D with an H217C in this box.

Anyone disagree, and if so why did DEC want their 11/05 S to use "D" model
core (D=parity) and not C (C=no parity)?  The PDP 11/40 I have uses C.


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