If the PAL can be read, it can easily be converted to a generic 16V8 GAL format.
So it appears that only two inputs (sourced by LM339 channels 1 and 2) and four outputs are used. A 2:4 decoder?
With only 2 direction inputs and 4 decoded outputs, there is only so much you can do.
Linked diagram shows it would be a simple decoder -- select neither rotation pair, forward rotation pair or reverse rotation pair. In case of both pair selected - default to...forward, left, none? I would assume none. For that we would need to see what is in the PAL.
It looks like this could have been done with two ICs - a dual 2:4 decoder and a hex inverter. They probably used a PAL to get both low cost ICs into a single IC... saves board space by a bit but would have cost them more per board to make.
An alternate thing this could have done was provide braking for the motor. When it hit stops (as sensed by two LM339 comparators), switch off the motor in that direction. Hard to tell without having schematics.
Looking at it more - the comparators selected which direction it was going. Left or right. There had to be something else to tell it when to start or stop.
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