Problems with my PDP 11/24 (was:Question about memory boards used n VAX 11/7xx)

From: Johnny Billquist <bqt_at_Update.UU.SE>
Date: Wed Dec 29 09:05:57 2004

On Wed, 29 Dec 2004 "Pierre Gebhardt" <> wrote:

>>> That's the info I found on the net from a 11/750 FAQ:
>>> "National Semiconductor Memory Systems: 1Mb memory boards. These
>>> boards have PWB 551109464-002 B
>>> PWA 980109464-001 D
>>> etched on them. They have a push-button switch for disabling the
>>> board, and a spare memory chip in a socket on the board. Board has
>>> green and yellow LEDS, which should normally both be on. Disabling
>>> the board causes the yellow LED to go out, and the red LED on the
>>> L0016 to come on, indicating bad memory configuration."
>> Those almost certainly aren't UNIBUS memory boards, but are
>> 11/750-specific boards.
> Thanks for this information, Patrick.
> I guess, I'll have to wait for such a VAX, I haven't one yet ;-)

Actually, the memory system in a VAX-11/750 are specific to that model.
It's not compatible with the VAX-11/780, nor the 11/730.

However, the memory backplane is compatible with the MK11 memory box for
the PDP-11/70. Unfortunately, the MK11 controller only deals with 256Kb
memory boards. So if you'd like to use these 1 Mb memory boards in an
11/70, you need a small hardware hack, and a small software hack.

The hardware hack is to tie four board select lines from the backplane
into to address lines for the memory card, and the software hack is to
reset all the ECC bits in the high 768K of each card, since the MK11
controller only clears ECC on the low 256K.

I have done both of these things on an 11/70 here in the past.


Johnny Billquist || "I'm on a bus
                                   || on a psychedelic trip
email: || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
Received on Wed Dec 29 2004 - 09:05:57 GMT

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