Toyota Inverter Clocked Serial Interface Protocol

This page is dedicated to use of Toyota inverters (Lexus / Camary / Gen3 Prius / Auris / Yaris) unmodified via the serial protocol (REQ, CLK, HTM, MTH). This page also contains wiring and connector information for the various models of Toyota Inverters.

Toyota Protocol

• REQ Request line from hybrid controller to Inverter
• CLK Clock signal from hybrid controller to Inverter (Constant 500KHz)
• HTM Hybrid controller to Inverter data frame
• MTH Inverter to Hybrid controller data frame

The number of bytes sent/received during a transfer will depend on the model of inverter, the table above outlines the number of bytes for the different inverter models.

Bus Transfer Sequence starts with the REQ line changing state

Toyota Serial example waveforms

Data logging Toyota Serial Protocol

Prius Gen3 PHV (Inverter model G9200-47200) has 105 bytes HTM and 140 bytes MTH

Toyota Inverter Connectors

Lexus GS450 / Camry

Gen3 Prius / Auris / Yaris

Prius Gen3  / Auris / Yaris Connector Body

HTM Data

HTM (Hybrid control unit To Motor control unit) data is required to make the motors spin. The following is a collection of what could be some of that data:

Typically the the frame is finished with a 16bit checksum of the preceding bytes, Least Significant Byte first.

EngineRPM is sent. A guess is this is so that the MCU can detect slip on the clutch-like slip disk that couples the engine flywheel to the hybrid transmission. On a Gen3 Prius this is sent at byte0 and is approximated by (MG1speed + MG2speed)/113. A more accurate calculation is (MG1speed + MG2speed*(143/145))*5/18/32. 143, 145, 5/18 are gear ratios in the transmission. 32 is probably so that rpm can fit into one byte.