Like the title said, I need some help identifying the chip in the picture:
since the board was manufactured by IPM and other chips are marked "IPM", the third row is probably an internal code that is useless for identification, but "SCL" is an actual IC prefix, so i think that "SCL1054-V4" is a valid part number.
I searched online for a datasheet but the only thing i found are the usual Chinese websites trying to sell me other chips (which I don't need). The National databooks I found weren't of much help.
I tried decapping one of those, and on the die I found a RCA logo and another code, but searching for this one I found even less data.
The chip is packaged in a PLCC-68 from the processor board of an Italian public payphone from the early '90s; if I had to guess I'd say it's some kind of communications chip (the phones are capable of talking to the phone company over the phone line using the HDLC protocol, but there isn't any kind of communications chip on the actual "line interface" board). I don't know how many of those were made, but I doubt that there were enough phones to justify a fully custom IC (especially considering that I have some boards that were made 3/4 years later that are vastly different; if they had a custom chip made I doubt they'd stop using it in the later revisions), so it's probably some off the shelf component.
Edit: I quickly checked the PCB with the multimeter and I found that the chip is connected to both the data and the address bus of the main processor; looking at the die (I would post a photo but with my microscope I can't really take a good picture of the whole die) it seems that it's got at least some amount of memory (roughly half the area of the chip). I don't think it's actually a memory chip because the phone has a 8K EPROM, a separate "configuration" 2K EPROM and a 2K SRAM chip, plus whatever RAM the MCU has onboard.
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