Pdp11/23+ EPROM upgrade

Johnny Billquist bqt at update.uu.se
Fri Feb 6 05:53:45 CST 2015

On 2015-02-06 12:41, Roe Peterson wrote:
>> On Feb 6, 2015, at 4:11 AM, Johnny Billquist <bqt at update.uu.se> 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.
>>> What are my replacement options?  I have a fairly capable programmer, it can probably handle anything with 64k capacity.
>> ??? I don't get it.
>> 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.
>> So why are you looking for a 64K chip? (27512 I would assume that would be...)
> 2716 = 16k bits = 2kbytes X 8 bits
> 2764 = 64k bits = 8kbytes X 8 bits
> The latest rom images for the 11/23+ require 8kbyte chips.

Ah, so 2764, not 64K bytes... Oh well... :-)
When did people start counting memory sizes in bits???


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