ADM1275-3ACPZ-R7 datasheet(29/48 Pages) AD

29 / 48 page

Data Sheet

ADM1275

Rev. D | Page 29 of 48

SLAVE ADDRESS

COMMAND CODE

BYTE COUNT = N

DATA BYTE 1

DATA BYTE N

DATA BYTE 2

SLAVE ADDRESS

COMMAND CODE

BYTE COUNT = N

DATA BYTE 1

DATA BYTE N

PEC

DATA BYTE 2

MASTER TO SLAVE

SLAVE TO MASTER

Figure 64. Block Read and Block Read with PEC

MASTER TO SLAVE

SLAVE TO MASTER

LOW DATA BYTE

DEVICE 1 ADDRESS

COMMAND CODE 1

HIGH DATA BYTE

ONE OR MORE DATA BYTES

LOW DATA BYTE

DEVICE 2 ADDRESS

COMMAND CODE 2

HIGH DATA BYTE

ONE OR MORE DATA BYTES

LOW DATA BYTE

DEVICE N ADDRESS

COMMAND CODE N

HIGH DATA BYTE

ONE OR MORE DATA BYTES

MASTER TO SLAVE

SLAVE TO MASTER

PEC 1

LOW DATA BYTE

DEVICE 1 ADDRESS

COMMAND CODE 1

HIGH DATA BYTE

ONE OR MORE DATA BYTES

PEC 2

LOW DATA BYTE

DEVICE 2 ADDRESS

COMMAND CODE 2

HIGH DATA BYTE

ONE OR MORE DATA BYTES

PEC N

LOW DATA BYTE

DEVICE N ADDRESS

COMMAND CODE N

HIGH DATA BYTE

ONE OR MORE DATA BYTES

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 I2C protocol point of view, a normal write command

consists of the following:

•

I2C 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)

•

I2C 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.

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