PDP-11/73 booting!

[Allison]

>
>Subject: Re: PDP-11/73 booting!
>   From: Pete Turnbull <pete at dunnington.plus.com>
>   Date: Mon, 12 Dec 2005 20:41:06 +0000 (GMT)
>     To: "General Discussion: On-Topic and Off-Topic Posts"<cctalk at classiccmp.org>
>
>On Dec 12 2005, 15:03, Allison wrote:
>
>> The BA23 came with a microPDP-11 backplane or one for the uVAX-II.
>> While the differences are small when used with care they are
>differnt.
>> For the PDP-11 use the MicroPDP11 backplane is desired as the uVAX
>> one has three slots that are CD wired for PMI bussed memory.
>> the DISK interface and distribution board in the back of the drive
>> cavity however are the same.
>
>All the ones I've ever seen in the field are the same regardless of
>whther for microPDP-11 or microVAX.  I can't see why the microVAX one
>would be different; the microPDP has the CD slots for PMI but the
>microVAX doesn't care -- it uses over-the-top connections for the
>memory.
>
>The BA23 backplane for a microPDP-11 is an H9278-A and does indeed have
>three slots Q22-CD followed by five serpentine Q22-Q22.  That's the
>same as my microVAX.  And that agrees with the Tech Manuals I have.

Ah, but it doesnt agree with mine. You can use the H9278 for Qbus -11
but if you want to maximize the slots there was a differnt early option
BA23 that had no CD slots(all were AB serpentine) as none of the 
processors before the PMI equipped 11/73 used PMI.  Early microPDP-11s
wer really 11/23Bs.  As a result there really were two similar but 
not exactly the same flavors. I know the gory details as my BA23 uVAX
was hacked from the uPDP-11 and I needed a differnt backplane 
(memory compatability) and the front pannel insert for the drive 
control was different.  At the time I was a Digit so getting the 
pieces from the systems lab was easy.


Allison