exxos's Atari, Amiga & retro forum

XK857J0 is not a version number; it is the Yamaha internal part catalog code for that specific mask ROM chip, commonly used during factory component production.

Because it is a factory-original mask ROM, it confirms your hardware is configured with the standard Version 1.x firmware base. This is excellent news for your Atari setup.

Yamaha used codes starting with "XK" or "XM" to track raw masked silicon inventory across their product lines. The XK857J0 chip contains the universal v1.20 series base code.

This is precisely the version Atari developers used when writing the Cubase Audio CBX hardware drivers.

mrbombermillzy wrote: 17 Jul 2026 12:24 @JezC After a bit of a search around:

XK857J0 is not a version number; it is the Yamaha internal part catalog code for that specific mask ROM chip, commonly used during factory component production.

Because it is a factory-original mask ROM, it confirms your hardware is configured with the standard Version 1.x firmware base. This is excellent news for your Atari setup.

Yamaha used codes starting with "XK" or "XM" to track raw masked silicon inventory across their product lines. The XK857J0 chip contains the universal v1.20 series base code.

This is precisely the version Atari developers used when writing the Cubase Audio CBX hardware drivers.

It appears the 'MAC' on the ICs is a bit misleading and was to denote it being part of a bundle sold for - but not specific to - the Macintosh.