Very handy- thanks! It looks very similar to the 3870.
The TI57 patent mentions a test pin, and describes how to dump the TMS1500 ROM. It looks much simpler than the TMS1000/1100! HrastProgrammer mentioned that a friend of his was able to dump the ROM, so I guess there is enough info in the patent. I'll probably still decap one, even though the instruction PLA is likely stock (since his emulator runs the ROM dump) and the output PLA would be easy to figure out.