Datasheet

Data Sheet ADM1275
Rev. D | Page 29 of 48
SrA SLAVE ADDRESS
AR
S AWSLAVE ADDRESS COMMAND CODE
A
BYTE COUNT = N
A
DATA BYTE 1
P
DATA BYTE NA
DATA BYTE 2
SrA SLAVE ADDRESS
AR
S AWSLAVE ADDRESS COMMAND CODE
A
BYTE COUNT = N
A
DATA BYTE 1
ADATA BYTE N P
PECA
DATA BYTE 2
MASTER TO SLAVE
SLAVE TO MASTER
08931-046
A
A
Figure 64. Block Read and Block Read with PEC
MASTER TO SLAVE
SLAVE TO MASTER
A LOW DATA BYTE AS AWDEVICE 1 ADDRESS COMMAND CODE 1
AHIGH DATA BYTE
ONE OR MORE DATA BYTES
A LOW DATA BYTE
A
Sr AWDEVICE 2 ADDRESS COMMAND CODE 2
A
HIGH DATA BYTE
ONE OR MORE DATA BYTES
A LOW DATA BYTE
ASr AWDEVICE N ADDRESS COMMAND CODE N
A P
HIGH DATA BYTE
ONE OR MORE DATA BYTES
08931-047
MASTER TO SLAVE
SLAVE TO MASTER
A
PEC 1
P
A LOW DATA BYTE
A
S AWDEVICE 1 ADDRESS COMMAND CODE 1
AHIGH DATA BYTE
ONE OR MORE DATA BYTES
APEC 2
A LOW DATA BYTE
ASr AWDEVICE 2 ADDRESS COMMAND CODE 2
AHIGH DATA BYTE
ONE OR MORE DATA BYTES
A
PEC N
A LOW DATA BYTE
A
Sr AWDEVICE N ADDRESS COMMAND CODE N
AHIGH DATA BYTE
ONE OR MORE DATA BYTES
08931-048
Figure 65. Group Command and Group Command with PEC
GROUP COMMANDS
The PMBus standard defines what are known as group
commands. Group commands are single bus transactions that
send commands or data to more than one device at the same
time. Each device is addressed separately, using its own address;
there is no special group command address. A group command
transaction can contain only write commands that send data to
a device. It is not possible to use a group command to read data
from devices.
From an I
2
C protocol point of view, a normal write command
consists of the following:
• I
2
C start condition
• Slave address bits and a write bit (followed by ACK from
the slave device)
• One or more data bytes (each of which is followed by ACK
from the slave device)
• I
2
C stop condition to end the transaction
A group command differs from a nongroup command in that
after the data is written to one slave device, a repeated start
condition is put on the bus followed by the address of the next
slave device and data. This continues until all the devices have
been written to, at which point the stop condition is put on the
bus by the master device.
The format of a group command and a group command with
PEC is shown in Figure 65.
Each device that is written to as part of the group command
does not immediately execute the command written. The device
must wait until the stop condition appears on the bus. At that
point, all devices execute their commands at the same time.
Using a group command, it is possible, for example, to turn
multiple PMBus devices on or off at the same time. In the case
of the ADM1275, it is also possible to issue a power monitor
command that initiates a conversion, causing multiple ADM1275
devices to sample together at the same time. This is analogous
to connecting the GPO1/
ALERT1
/CONV pins together and
configuring the pin in the convert (CONV) mode to drive the
power monitor sampling.