ADP1055ACPZ-R7 datasheet(47/140 Pages) AD

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Data Sheet

ADP1055

Rev. A | Page 47 of 140

PMBUS DIGITAL COMMUNICATION

The PMBus slave with PEC allows a device to interface to a

PMBus compliant master device, as specified by the PMBus

Power System Management Protocol Specification (Revision 1.2,

September 6, 2010). The PMBus slave is a 2-wire interface that

can be used to communicate with other PMBus compliant

devices and is compatible in a multimaster, multislave bus

configuration. The PMBus slave can communicate with master

PMBus devices that support packet error checking (PEC), as

well as with master devices that do not support PEC.

FEATURES

The function of the PMBus slave is to decode the command

sent from the master device and respond as requested.

Communication is established using an I2C-like 2-wire interface

with a clock line (SCL) and data line (SDA). The PMBus slave is

designed to externally move chunks of 8-bit data (bytes) while

maintaining compliance with the PMBus protocol. The PMBus

protocol is based on the SMBus Specification (Version 2.0,

August 2000). The SMBus specification is, in turn, based on the

Philips I2C Bus Specification (Version 2.1, January 2000). The

PMBus incorporates the following features:



Slave operation on multiple device systems



7-bit addressing



100 kbits/sec and 400 kbits/sec data rates



Packet error checking



Support for the Group Command Protocol



Support for the Alert Response Address Protocol with

arbitration



General call address support



Support for clock low extension (clock stretching)



Separate multiple byte receive and transmit FIFO



Extensive fault monitoring

OVERVIEW

The PMBus slave module is a 2-wire interface that can be used

to communicate with other PMBus compliant devices. Its transfer

protocol is based on the Philips I2C transfer mechanism. The

ADP1055 is always configured as a slave device in the overall

system. The ADP1055 communicates with the master device

using one data pin (SDA) and one clock pin (SCL). Because the

ADP1055 is a slave device, it cannot generate the clock signal.

However, it is capable of clock-stretching the SCL line to put the

master device in a wait state when it is not ready to respond to

the master’s request.

Communication is initiated when the master device sends a

command to the PMBus slave device. Commands can be read

or write commands, in which case data is transferred between

the devices in a byte wide format. Commands can also be send

commands, in which case the command is executed by the slave

device upon receiving the stop bit. The stop bit is the last bit in a

complete data transfer, as defined in the PMBus/SMBus/I2C

communication protocol. During communication, the master

and slave devices send acknowledge or no acknowledge bits as a

method of handshaking between devices.

In addition, the PMBus slave on the ADP1055 supports packet

error checking (PEC) to improve reliability and communication

robustness. The ADP1055 can communicate with master PMBus

devices that support PEC, as well as with master devices that do

not support PEC. See the SMBus specification for a more detailed

description of the communication protocol.

When communicating with the master device, it is possible for

illegal or corrupted data to be received by the PMBus slave device.

In this case, the PMBus slave device should respond to the

invalid command or data, as defined by the PMBus specification,

and indicate to the master device that an error or fault condition

has occurred. This method of handshaking can be used as a first

level of defense against inadvertent programming of the slave

device that can potentially damage the chip or system.

The PMBus specification defines a set of generic PMBus

commands that is recommended for a power management

system. However, each PMBus device manufacturer can choose

to implement and support certain commands as it deems fit for

its system. In addition, the PMBus device manufacturer can

choose to implement manufacturer-specific commands whose

functions are not included in the generic PMBus command set.

The list of standard PMBus and manufacturer-specific commands

can be found in the Standard PMBus Commands Supported by

the ADP1055 section and Manufacturer Specific Commands

section.

TRANSFER PROTOCOL

The PMBus slave follows the transfer protocol of the SMBus

Specification (Version 2.0), which is based on the fundamental

transfer protocol format of the Philips I2C Bus Specification

(Version 2.1). Data transfers are byte wide, lower byte first. Each

byte is transmitted serially, most significant bit (MSB) first.

Figure 69 shows a basic transfer.

Figure 69. Basic Data Transfer

For an in-depth discussion of the transfer protocols, see the

SMBus and I2C specifications.

7-BIT

ADDRESS

R/W

A...

8-BIT DATA

= MASTER-TO-SLAVE

= SLAVE-TO-MASTER

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