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looking for reference manual to identify old HP ROM 1818 2173A (2770C)

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jorgeh:
Hi

I was hoping if someone has an old HP spare parts guide. it came from an Hewlett Packard 34721B BCD Module.
I found the equivalent for the display IC 1990 0408 and decade counter. but i ahvent found any reference on internet related to 1818 2173A
if anyone has an idea what would be the equivalent. it would be much preciated.

martinr33:
That family of units appears to be pre-microprocessor. Those date codes are from the 1970s, before there was a plan for the 1980s.

This site has some useful information. https://www.barbouri.com/2022/07/11/hewlett-packard-34721b-bcd-module/


The device may be  some form of masked ROM.

You can probably replace it by wiring in a 2716. For that era, it is likely a 3 rail device. Or you may need to add a second device to boost the data width - 28 pins seems like a lot.

If someone has schematics, that would be useful.

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