Playing with HP2640B

Curious Marc curiousmarc3 at
Wed Dec 6 02:28:39 CST 2017

We just dumped the enhanced character ROMs from a HP2645. 8k bipolar mask ROMs, 90 ns (they need to be fast since they are used as video RAM really). I read them on the Data IO using their PROM equivalent, AMD 27S181. The microvectors sets (line set and large character sets) are 9 bits. The 9th bit comes out on pin 18 in place of an enable pin in the more conventional 8-bit version. I read them in two passes, wiring the pin for bit 9 in place of bit 8 pin the second time around. 9-bit mask ROMs! Why not 5-legged pigs while you are at it. Then we found that even HP had misgivings about their weird 9-bit ROM choices, must have cost a fortune. Carl had a later rev board that had 8-bit version of the microvector sets, where the board has electronics to create an emulated 9th bit by shifting all the bits out and duplicating bit 0. Better yet, we burned some new 8-bit bipolar PROMs (Harris 7681), emulated the bit shifting on my older rev of the board by cross-wiring, and added new large character sets to my terminal! That was fun.

On Dec 5, 2017, at 1:36 PM, Brent Hilpert via cctalk <cctalk at> wrote:

On 2017-Dec-05, at 1:20 PM, Brent Hilpert via cctalk wrote:

>> On 2017-Dec-05, at 1:08 PM, Mattis Lind wrote:
>> 2017-12-05 20:44 GMT+01:00 Brent Hilpert via cctalk <cctalk at>:
>>> On 2017-Dec-05, at 9:14 AM, Mattis Lind via cctalk wrote:
>>>> Does the 27S82 have any equivalents that I could look up instead in the
>>>> device list?
>>> FWIW, 27S82 is listed in the 1982 IC Master as
>>>     AM27S82M:   TTL 1024*8 ROM, 275nS access, OC outputs, 24 pin, 5V supply
>>> So half the size of a 2716.
>>> The book lists PROMs and ROMs separately, so it was probably mask-programmed.
>>> (M would be for mil temp going by other AMD numbers.)
>> I would think bipolar PROM since rest of the AMD 27S series were bipolar PROMs. I will check this weekend if I can find an old AMD databook.
> The ref did specify it as TTL, so yes, bipolar.

Oh, as for being PROM vs ROM, I'm just going by the way things are listed in the ref.
It lists different 27Sxx devices under PROM vs ROM,
for example 27S180, 27S181 are 1024*8 listed under PROM, but 27S80, 27S81, 27S82, 27S83 are 1024*8 listed under ROM.
It's possible they're mis-listed of course, but manufacturers often did make equivalent devices as both fusible and mask,
I don't know what AMD did for series names in that regard.

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