[nicole_express]

The Signetics 2650 found its way into a bunch of arcade games by lieu of British company Century Electronics. I have a conversion kit of theirs installed into a Donkey Kong Jr. board, which outright replaces DK Jr.'s Z80 with a daughterboard containing the CPU. Always wondered why they chose that in particular, it's not a very common chip, and just using the Z80 that was there and replacing the ROMs was the more common option for conversion kits like that.

[jockm]

The 2650 was one of the first microprocessors on the market you could buy, it was shockingly simple to design, and had some dedicated I/O lines. Look up the reference schematic and compare to what a 6502 or Z80 needs. It was used in a lot of early embedded systems. It makes sense in that light

[classichasclass]

Zaccaria pinballs I think used it pretty heavily as well. Again, no clear explanation there either.

[duskwuff]

Given the era, I wouldn't be surprised if it came down to "someone on the development team liked that part". (Or "someone in the purchasing department got a bunch of them really cheap".)