I start to decode the U51 TPAL2 PAL16R8 today.  Made an interesting discovery, I notice that the RAM CASL and CASU signals are swapped. Scratching my head, thinking why ?.

This must have been a slight design error and the designer decided to correct the error within the PAL. So the UDS signal turns into CASL and LDS  is CASU.

Here is a quick snap shot of signal don't panic the timing is not correct, I stimulated the clock signals with the logic analysers wave generator. More to come.