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
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
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 as first byte where 1bit = 32rpm. This 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 as seen in this video. 32 is probably so that rpm can fit into one byte and is easily accomplished by bit shift to the right (32 = 2^5).
| Data type | Prius Gen3 | GS450h |
|---|---|---|
| Checksum (sum of all preceding bytes) LSB first | [98,99] | [78,79] |
| Engine RPM | [0] | [0] |
| MG1 Torque Request*4 | [91,92] | [75,76] |
| MG1 Torque Request | [5,6] [11,12] | [5,6] [11,12] |
| MG2 Torque Request | [30,31] [36,37] | [26,27] [32,33] |
| Battery Regen Power Limit | [76,77] | [63,64] |
| Battery Discharge Power Limit | [78,79] | [65,66] |
| Sequential Number | [94] |