Pdp11/23+ EPROM upgrade

Johnny Billquist bqt at update.uu.se
Fri Feb 6 05:55:57 CST 2015

On 2015-02-06 12:35, Pete Turnbull wrote:
> On 06/02/2015 10:11, Johnny Billquist wrote:
>> On 2015-02-05 19:49, Roe Peterson wrote:
>>> I want to update the EPROMs on my 11/23+, which currently has 2716s.
>>> I'm going to need 64k chips, and I understand 2764s won't work on this
>>> board.
> Correct, wrong physical size.  DEC used Motorola MCM68766.
>> 64K chips? The 11/23 currently uses the 2716, which is what? 2K (bytes)?
>> I doubt there are any more address lines going to that chip in the first
>> place, and second, the memory is mapped in the I/O space which have a
>> total of 8K, and that should cover not only the boot rom, but also all
>> CSRs of all devices you have in the machine. A 64K chip is going to be
>> totally meaningless.
> Not so.  Only the earliest release 11/23+ (KDF11-BA) used 2KB firmware;
> all the later versions (there are at least six) used 8KB and had more
> functionality.  The M8189 board is designed to take either.  In both
> cases, the ROM is paged exactly as it is in a BDV11, and only 256 bytes
> are visible at a time.  J22/J23/J24 are the links used to configure the
> sockets, and you'll find the settings on page 2-8 of the KDF11-BA Users
> Guide.  Seven address bits to the ROMs come from the bus, six are
> provided by paging registers on the CPU board, for a total of 13 address
> bits, or 8KB address space.

Ok. I wasn't aware that the 11/23 had a page selection mechanism for the 
boot rom.

>> So why are you looking for a 64K chip? (27512 I would assume that would
>> be...)
> 2764.  He meant 64K bits.

That was a different story, yes. :-)


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