Understanding the SENT Interface – sidebar

Sending a slow message using Enhanced Serial Messaging Format (either one 12-bit data word or one 16-bit data word) requires 18 fast channel message frames. Similar to the Slow Channel Message, the Enhanced Serial Messaging data are sent 2 bits at a time and comprise bit 3 and bit 2 of the status nibble.

The top of the figure below shows how the data are organized for the 12-bit mode with the configuration bit (i.e., the C bit in the “Serial Data (Status Bit 3)” row) set to logic 0. The 12-bit mode supports a 6-bit CRC/checksum, 12 bits of slow-channel data and an 8-bit message ID. Unused data fields are hard-coded with logic 1 or 0 and are used to identify the start of a slow channel message as indicated by a string of six logic 1’s.

The bottom of the figure shows how the data are organized for 16-bit mode, which is selected by setting the configuration (C) bit to logic 1. The 16-bit mode supports a 6-bit CRC/checksum, 16-bits of slow-channel data and a 4-bit message ID. Unused data fields are hard-coded with logic 1 or 0.

Fig.: The Enhanced Serial Message Format differs for 12-bit (top) or 16-bit (bottom) message lengths.