I recognized the "MM" prefix as an old National Semiconductor PMOS part - I remember several digital clock and calculator chips in that series. Anyway, I googled this p/n and it's a curious little mask programmed 1024 bit ROM dating to the mid 70's. It could be used as 128 x 8 (probably what they used in this case) or 256 x 4. Seems like the ROM would easily fit the quick brown fox message, or, as you stated be programmed to translate baudot to ASCII (or vice versa). I don't think a processor would've been necessary - the thing could've been driven with some counters and start/stop logic. I wonder if the the big white chip is a UART, or maybe a UART with a built-in baud rate generator...? That also seems unnecessary, but who knows. Wonder what the switch on the far right (off / 10^5 / 10^4 / 10^3) does?

Cool find!

Keith

On Tuesday, January 24, 2023 at 08:41:24 AM CST, Jeffrey Golas <[email protected]> wrote:

Thought you guys and gals might find this interesting...I volunteer on Battleship NJ and found this tucked away. Appears to be Navy-like but mentions "project" on it, serial #3 lol. Other than WMS on the board theres no manufacturer.

Its a RTTY/Teletype message generator that does the "quick brown fox" message. Whats really interesting is that all that is based on ONE chip whose sole purpose is exactly that. A MM5220DF. Other chips in that series have similar purposes, like ASCII-BAUDOT conversion.

Theres what looks like a white CPU, but Icant find any docs on it. It almost looks like something they had a surplus of, and with no rom, possibly wired it as a NOP (no-operation) so that it would just be an 8 bit counter. I think anyway.

It does seen to work after cleaning all the switches, I plan to test on the loop. All it does is keying via a solid state relay. I tried piping my signal gen through it but Fldigi couldnt decode.

Jeff KC3GJX