Pdp11/23+ EPROM upgrade

Brent Hilpert hilpert at cs.ubc.ca
Fri Feb 6 15:16:16 CST 2015

On 2015-Feb-06, at 3:53 AM, Johnny Billquist wrote:
> 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???

Oh, at least as early as the mid-70s, with the 2708 (1KByte).

Yes, I too wish they had used bytes for eprom sizes.

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