Automatic Pec Addition - Texas Instruments UCD3138 Technical Reference Manual

PMBus Slave Mode Command Examples
The write sequence at the beginning of a read is basically the same as the write sequence at the
beginning of this section. The difference is that RPT_START is set instead of EOM and PEC_VALID. The
same rule applies to longer writes followed by a repeated start. Any number of bytes written, followed by a
repeated start, and they will be the same as a standard write sequence, except that they end with a
repeated start, rather than an EOM.

10.3.14 Automatic PEC Addition

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.
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PMBus Interface/I2C Interface
Copyright © 2016, Texas Instruments Incorporated
SNIU028A – February 2016 – Revised April 2016
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