ADP1047ARQZ-R7 datasheet(36/84 Pages) AD

36 / 84 page

ADP1047/ADP1048

Data Sheet

Rev. 0 | Page 36 of 84

SLAVE

ADDRESS

SLAVE

ADDRESS

COMMAND

CODE

BYTE COUNT

= N

DATA BYTE 1

MASTER TO SLAVE

SLAVE TO MASTER

DATA BYTE N

Figure 42. Block Read Protocol

Clock Generation and Stretching

The ADP1047/ADP1048 are always PMBus slave devices in the

overall system; therefore, the device never needs to generate the

clock, which is done by the master device in the system. How-

ever, the PMBus slave device is capable of clock stretching to

put the master in a wait state. By stretching the SCL signal

during the low period, the slave device communicates to the

master device that it is not ready and that the master device

must wait.

Conditions where the PMBus slave device stretches the SCL line

low include the following:

•

The master device is transmitting at a higher baud rate

than the slave device.

•

The receive buffer of the slave device is full and must be

read before continuing. This prevents a data overflow

condition.

•

The slave device is not ready to send data that the master

has requested.

Note that the slave device can stretch the SCL line only during

the low period. Also, whereas the I2C specification allows

indefinite stretching of the SCL line, the PMBus specification

limits the maximum time that the SCL line can be stretched,

or held low, to 25 ms, after which the device must release the

communication lines and reset its state machine.

GENERAL CALL SUPPORT

The PMBus slave is capable of decoding and acknowledging

a general call address. The PMBus device responds to both its

own address and the general call address (0x00). The general

call address enables all devices on the PMBus to be written to

simultaneously.

Note that all PMBus commands must start with the slave

address with the R/W bit cleared (set to 0), followed by the

command code. This is also true when using the general call

address to communicate with the PMBus slave device.

FAST MODE

Fast mode (400 kHz) uses essentially the same mechanics as

the standard mode of operation; the electrical specifications

and timing are most affected. The PMBus slave is capable of

communicating with a master device operating in standard

mode (100 kHz) or fast mode.

FAULT CONDITIONS

The PMBus protocol provides a comprehensive set of fault

conditions that must be monitored and reported. These fault

conditions can be grouped into two major categories: commu-

nication faults and monitoring faults.

Communication faults are error conditions associated with the

data transfer mechanism of the PMBus protocol. Monitoring

faults are error conditions associated with the operation of the

PMBus device, such as output overvoltage protection, and are

specific to each PMBus device. These fault conditions are

described in the Power Supply System and Fault Monitoring

section.

TIMEOUT CONDITION

A timeout condition occurs if any single SCL clock pulse is held

low for longer than the tTIMEOUT of 25 ms (min). Upon detecting

the timeout condition, the PMBus slave device has 10 ms to abort

the transfer, release the bus lines, and be ready to accept a new

start condition. The device initiating the timeout is required to

hold the SCL clock line low for at least tTIMEOUT MAX = 35 ms,

guaranteeing that the slave device is given enough time to reset

its communication protocol.

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