SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
For PMBus commands, the UCD also provides for automatic addition of a PEC byte at the end. When writing the last bytes in the message to the TXBUF, first set the TX_PEC bit. The interface will automatically send out the number of bytes in TXBUF, and then add a PEC byte at the end. This option should not be used if the master is not guaranteed to send a stop signal after the PEC. If the system requires that the UCD continue to transmit bytes after the PEC, the PEC should be calculated in firmware and added as a normal data byte. The UCD PMBus/I2C hardware assumes that the PEC will be the last byte in the message.