SPRUJ79 November 2024 F29H850TU
The Enhanced Serial Message Format has a larger data field and set of message IDs available than the Short Serial Message Format. The serial message frame consists of a configuration bit and configurable 20-bit payload. The Enhanced Serial Message Format allows for this 20-bit payload to be configurable as an 8-bit message ID with 12-bit slow data or a 4-bit message ID with 16-bit slow data. The serial data is transmitted in bit 2 and 3 of the status and communication nibble from 18 consecutive data frames, similar to the Short Serial Message Format. The serial message is interleaved in 18 frames, so SENT keeps track and extracts the status and communication bits from every frame. Thus, by the 18th frame the complete message is received, given there are no errors.
The start of a serial message frame is indicated by "01111110" in bit 3 of the status and communication nibble. The first 1 in the sequence indicates the first nibble in the serial message frame. Bit 3 of the status and communication nibble must be 0 for message 7, 13, and 18. Bit 3 of the status and communication nibble of frame 8 is the C bit, which chooses the configuration.
The advantage to using the Enhanced Serial Message Format is that either a larger selection of message IDs can be used or more slow data can be transmitted using bit 3 of the status and communication nibble pulse, but in both cases there is more slow data received than the Short Serial Message Format.