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Tube🌞Time

there's something weird about the markings on the bottom of the chip
24 February at 23:08 | Open on mastodon.social
14 comments
Robert Petersen :pacman:
Tube🌞Time

got a better die photo. i think i know what this chip is.
26 February at 2:10 | Open on mastodon.social
Tube🌞Time

the cells are way too simple to be SRAM or RAM. i think this is a ROM.
26 February at 2:11 | Open on mastodon.social
Tube🌞Time

the array is 32x32, and there seem to be four outputs at the bottom of the array. that would make this a 256x4 ROM.
26 February at 2:12 | Open on mastodon.social
Tube🌞Time

pin 9 (and a bunch of others) are inputs. they go through a series resistor, a diode clamp (not visible here) and into a double set of inverters. this creates a buffered version of the input and an inverted version.
26 February at 2:13 | Open on mastodon.social
Tube🌞Time

pins 3, 4, 5, and 6 appear to have large output driver transistors.
26 February at 2:15 | Open on mastodon.social
Tube🌞Time

looks like a perfect match to the MCM14524! unfortunately it is a mask ROM: "This device is ordered as a factory special with its unique pattern specified by the user."
26 February at 2:19 | Open on mastodon.social
Tube🌞Time

how fun, you can specify the memory contents by mailing them four punch cards.
26 February at 2:21 | Open on mastodon.social
Foone🏳️‍⚧️

@tubetime I think Fujitsu (or maybe it was Toshiba?) was later accepting 8mm backup tapes. Handy for the bigger ROMs

26 February at 3:12 | Open on digipres.club
PhDog 🇮🇪
waldi

@tubetime I immediately thought about mask rom. But I thought they changed just the metal layer, and I did not see any difference between cells.

26 February at 10:21 | Open on chaos.social
Tube🌞Time

@waldi this is most likely a diffusion ROM so it would be difficult to see

26 February at 14:55 | Open on mastodon.social
Dustin

@tubetime I learned about factory ROMs but I’ve never used one. Very cool!

26 February at 3:17 | Open on geekdom.social
djb_rh

@tubetime The case looked like ROM of the day, too.

26 February at 2:49 | Open on mastodon.social
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