Can S9S12XS256J0CAE completely replace S9S12XS128J1CAE? Are the two just the difference in flash size?
If I don't have this S9S12XS128J1CAE, can I use S9S12XS256J0CAE instead?
Not only the Flash size but the SRAM too:
There are a few different specifications,
Table A-5. Thermal Package Characteristics (9S12XS256)
Table A-6. Thermal Package Characteristics (9S12XS128)
Table A-12. Run and Wait Current Characteristics
These two parts have different masks:
The RM specifies different part ID numbers:
Each mask revision has a different errata document: