Similar to I
2
C, PMBus is a variable length packet of 8-bit data bytes, each with a receiver acknowledge,
wrapped between a start and stop bit. The first byte is always a 7-bit
target address
followed by a
write
bit,
sometimes called the
even address
, that identifies the intended receiver of the packet. The second byte is an
8-bit
command
byte, identifying the PMBus command being transmitted using the respective command code.
After the command byte, the transmitter either sends data associated with the command to write to the receiver
command register (from least significant byte to most significant byte; see also
), or sends a new start
bit indicating the desire to read the data associated with the command register from the receiver. Then the
receiver transmits the data following the same least significant byte first format; see also
Table 7-7. PMBus Update Sequence
MSB
....
LSB
ACK
MSB
...
LSB
ACK
MSB
...
LSB
ACK
MSB
...
LSB
ACK
Address (A) byte
Command byte
Data byte - LSDB
Data byte - MSDB
(Optional)
DB [31:24]
DB [23:16]
DB [15:8]
DB [7:0]
Table 7-8. PMBus Read Sequence
S
MSB
…
R/W
(0)
ACK
MSB
…
LSB
ACK
Sr MSB …
R/W
(1)
ACK
MSB
…
LSB
ACK
MSB
…
LSB
ACK
Address byte
Command byte
Sr
Address byte
LSDB
MSDB (Optional)
From controller
Target
From controller
Target
From controller
Target
From target
Controller
From target
Controller
The DACx3202 I
2
C interface implements some of the PMBus commands.
shows the supported
PMBus commands that are implemented in DACx3202.The DAC uses DAC-X-MARGIN-LOW, DAC-X-MARGIN-
HIGH bits, SLEW-RATE-X, and CODE-STEP-X bits for PMBUS-OPERATION-CMD-X. To access multiple
channels, write the PMBus page address specified in
to the PMBUS-PAGE register first, followed
by a write to the channel-specific register.
Table 7-9. PMBus Operation Commands
REGISTER
PMBUS-OPERATION-CMD-X[15:8]
DESCRIPTION
PMBUS-OP-CMD-X
00h
Turn off
80h
Turn on
94h
Margin low
A4h
Margin high
The DACx3202 also implement PMBus features such as group command protocol and communication timeout
failure. The CML bit in the PMBUS-CML register indicates a communication fault in the PMBus. This bit is reset
by writing 1.
To get the PMBus version, read the PMBUS-VERSION register.
SLASF47 – MAY 2022
38
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