Units of Transmitter Delay Compensation Offset TDCO

Issue Details

Transmitter Delay Compensation Offset (TDCO) is a property of the baud rate used in automotive communication.

TDCO is used to adjust when the CAN controller samples the transmitted bit to account for the delays from the controller (transmit) to the transceiver and then back to the controller (for sampling).

Solution

The units are in clock periods to the CAN controller. Using NI Automotive Hardware, the value of TDCO is 25ns. For example, with a controller running at 40 MHz, the unit of time would be 25 ns.

This adjustment is crucial at fast baud rates because the delays are significant relative to the bit rate, and proper alignment is necessary. While the general time to go to and from the transceiver is automatically detected by the hardware, TDCO provides an additional time parameter to optimize the sampling moment.

A TDCO value of 0 means sampling occurs right at the starting edge, and each additional 25 ns shifts the sampling point further. Typically, TDCO is set to align with the sample point, such as setting TDCO to 3 for a 75% alignment if the Tq is 25 ns and there are 4 Tq in the measurement. As baud rates decrease, further adjustments are needed, although at very low baud rates, compensation may no longer be necessary.