DATA_RDY
1
4
RD_BYTE_COUNT
Write to ACK
3
2
A
Command
8
A
1
1
PMBus Slave Mode Command Examples
361
SNIU028A – February 2016 – Revised April 2016
Copyright © 2016, Texas Instruments Incorporated
PMBus Interface/I2C Interface
4. The ACK will be cleared by the end of the ACK sequence.
The manual slave ACK has no effect on later bytes in the sequence, so there is no need to show full
sequences with manual slave ACK at the beginning. All sequences will be the same as if there is an
automatic slave ACK after step 4 in the figure above.
10.3.7 Manual Command ACK
If the MAN_CMD bit is set, the firmware will be required to manually acknowledge every command. This
should only be used if there is a requirement for NACK of invalid commands. Here is the sequence for this
byte:
Figure 10-9. Manual ACK Command
Manual command timing is actually exactly the same as the timing for a byte when the RXBUF needs to
be read:
1. t
DRDY
after the falling clock for the last bit of the command, DATA_RDY is set, and 1 is put into
RD_BYTE_COUNT.
2. The firmware reads PMBST, and then reads the command from RXBUF
3. The firmware writes a 1 or a 0 to the ACK register, depending on whether the command is accepted or
not. t
ACKWRITE
after the write to ACK, any clock stretch is ended. If the firmware is fast enough, clock
stretching will not occur at all.
4. The ACK bit is cleared by the end of the ACK signal on the bus.
10.3.8 Read Messages with Full Automation
Like write messages, read messages can be handled most efficiently by using the full 4 bits of the buffer,
TXBUF in this case. With automatic address acknowledgement, the Read command can be handled
almost as efficiently as the write command. This is especially true of the simplest case, which is I2C
specific, not supported in the PMBus – read only. Here is the sequence diagram: