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PMBus Slave Mode Command Examples
1
S
EOM
PEC_VALID
DATA_RDY
RD_BYTE_COUNT
EOM
PEC_VALID
DATA_RDY
RD_BYTE_COUNT
All of these diagrams have the same basic operation – at the end of the message the firmware simply has
to read the RXBUF and set the ACK bit, and process the message. The only difference is the number put
in RD_BYTE_COUNT, and the value put in PEC_VALID. The command byte, any data bytes, and the
PEC all are included in the RD_BYTE_COUNT.
10.3.3 Quick Command Write
The Quick Command has only the address byte with the R/W bit cleared to indicate a write. It is just the
same as the messages above, except the DATA_RDY and RD_BYTE_COUNT bits will not be set. Since
there is no data, only the EOM bit will be set. Ignore PEC_VALID.
10.3.4 Writes of 4 Bytes or More With Full Auto Acknowledge
At 4 bytes counting command, data, and PEC, if any, the 4 byte RXBUF will be full. The RXBUF must be
read, and the ACK bit set, before the PMBus hardware can accept more data. If the firmware is quick
enough, there will be no clock stretching. The PMBus hardware automatically provides clock stretching on
the ACK for the 4th byte, if it is necessary. Here is the timing diagram:
358
PMBus Interface/I2C Interface
7
1
1
Address Wr A
Command
Figure 10-4. Write Command and Byte - with PEC
1
7
1
1
S
Address Wr A
Figure 10-5. Write 2 Bytes with no PEC
Copyright © 2016, Texas Instruments Incorporated
8
8
1
A Data Byte
8
1
A Data Byte
Command
SNIU028A – February 2016 – Revised April 2016
www.ti.com
1
8
1
1
A
A
P
PEC
1
8
1
1
A
P
1
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