38880-57B40 TCM

This is a Transmission Control Unit (TCM) for an Aisin Warner 4-sp auto transmission. I picked this up cheap because the seller didn't know what it was. The TCM has a one-wire bi-directional serial data link (SDL) similar to the Suzuki EFI ECU but the protocol is very different. The TCM broadcasts messages continuously. There are 10 messages, each one three bytes long consisting of a header field, an address field and a data field. The baud rate is approx. 15625bps.

The processor is a 76C40AP, the silkscreen identifies it as a TMP76C40 pointing to this being a Toshiba manufactured device. The 76C40 was also fitted in Denso engine management systems and is a lower pincount variant of the processors fitted in many Mitsubushi engine ECUs.
My analysis has determined that the processor is backwardly compatible with the MC6801 but has many more advanced features imcluding additional memory manipulation instructions, Y-indexing and a little more RAM. The E-clock runs at 1/6th of the crystal frequency, and a less obvious difference is that some of the instructions use different numbers of clock cycles to execute.

The processor has either masked ROM or OTP memory so I used my Rom Reader PCB to download the firmware which I then ran through a dissasembler, surprisingly the AW firmware uses only 6801 compatible instructions indicating that the processor was used as a straight replacement for a 6801.