ST AN2511 APPLICATION NOTE

AN2511

Application note

PMBusTM interface using ST7 I2C

Introduction

The PMBusTM (power management bus) is an open standard protocol that defines a means
of communicating with power conversion and other devices. The PMBus protocol helps to
establish the first truly open communications standard for the digital control of power
systems. Implemented over the industry-standard SMBus (system management bus) serial
interface, the PMBus protocol facilitates the programming, control and real-time monitoring
of compliant power conversion products.

This application note describes how to use the ST7 I
communication. The firmware of this application performs the PMBus bus protocols
mentioned in PMBusTM power system management protocol specification v1.0. The device
chosen here is ST72264G1 which has multi-master I
as the PMBus master. It controls the PMBus compatible slaves. The firmware described in
this application note is in C language.

To show the PMBus capabilities of ST7, a dedicated demonstration board is developed. This
board consists of the ST72F264G1 microcontroller and it works with PC hyperterminal. The
objective of this demonstration board is to show to the user the features and capabilities of
PMBus features using ST7 I
results of this demonstration board interfaced with Artesyn's PMBus module are shown in
this application note.

2

C peripheral, to support the standard PMBus commands. The

2

C peripheral for PMBus

2

C capability. This microcontroller acts

August 2010 Doc ID 13286 Rev 2 1/43

www.st.com

Contents AN2511

Contents

1 PMBus introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.1 PMBus protocol description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.1.1 SMBus version 1.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.1.2 Extensions to SMBus version 1.1 specification . . . . . . . . . . . . . . . . . . . . 6

1.2 Hardwired signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2.1 Electrical interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2.2 Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 Implementation of PMBus using ST7 I2C . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1 Firmware architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.1 I2C initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.2 Slave address and command code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.3 Read and write operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 PMBus commands and source code . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1 PMBus commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.2 Source code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.3 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.4 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4 PMBus interfacing results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.1 Interfacing with Artesyn module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.2 Interfacing with SiLabs module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

5 PMBus demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5.1 System requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5.2 Software setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5.3 Hardware setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

6 Using the demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6.1 Normal operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6.1.1 Selection of communication speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6.1.2 Selection of packet error checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

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AN2511 Contents

6.1.3 Selection of slave address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6.1.4 Selection of read/write mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6.1.5 Single read mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6.1.6 Continuous read mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

6.1.7 Write mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

6.1.8 Group command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

6.2 Error conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

6.2.1 Invalid command code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

6.2.2 Communication timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

7 Hardware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

7.1 Schematic and layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

7.2 Bill of materials (BOM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

7.3 Demonstration board photo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Appendix A Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

A.1 RS232 configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Doc ID 13286 Rev 2 3/43

List of tables AN2511

List of tables

Table 1. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table 2. ON_OFF_CONFIG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table 3. CLEAR_FAULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table 4. RESTORE_DEFAULT_ALL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table 5. STORE_USER_ALL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table 6. VOUT_MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table 7. VOUT_COMMAND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 8. VOUT_MAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 9. VOUT_MARGIN_HIGH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 10. VOUT_MARGIN_LOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 11. VOUT_OV_WARN_LIMIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 12. VOUT_UV_WARN_LIMIT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 13. IOUT_OC_FAULT_LIMIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 14. IOUT_OC_WARN_LIMIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 15. OT_FAULT_LIMIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 16. OT_FAULT_RESPONSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 17. OT_WARN_LIMIT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 18. TON_DELAY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 19. TON_RISE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 20. TOFF_DELAY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 21. TOFF_FALL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 22. STATUS_BYTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 23. STATUS_WORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 24. STATUS_VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 25. STATUS_IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 26. STATUS_TEMPERATURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 27. STATUS_MFR_SPECIFIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 28. READ_VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 29. READ_IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 30. READ_TEMPERATURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 31. PMBUS_REVISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table 32. MFR_ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table 33. MFR_MODEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table 34. MFR_REVISION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table 35. MFR_LOCATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 36. MFR_DATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 37. MFR_SERIAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 38. MFR_SPECIFIC_00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 39. MFR_SPECIFIC_01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Table 40. MFR_SPECIFIC_02 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Table 41. PMBus interfacing with Artesyn module: results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Table 42. PMBus interfacing with SiLabs module: results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Table 43. Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Table 44. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4/43 Doc ID 13286 Rev 2

AN2511 List of figures

List of figures

Figure 1. Interface diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 2. Flowchart: I

Figure 3. Flowchart: data length calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 4. Flowchart: read operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 5. Flowchart: write operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 6. PC hyperterminal application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 7. Baud rate configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 8. Hyperterminal settings - ASCII setup configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 9. Hyperterminal message to show company name and selection of communication speed 30

Figure 10. PEC selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 11. Slave address entry message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 12. Wrong slave address entry - response 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 13. Wrong slave address entry - response 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 14. Options to select read/ write mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 15. Single read operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 16. Continuous read operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 17. Write mode command code entry message from hyperterminal . . . . . . . . . . . . . . . . . . . . 32

Figure 18. Write mode data entry message from hyperterminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 19. Write mode operation example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 20. Read operation to check data writing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 21. Group command code entry message from hyperterminal. . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 22. Group command operation example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 23. Invalid command message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 24. Example of invalid command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 25. Communication timeout message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 26. Demonstration board schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 27. Top view layout of the demonstration board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 28. Bottom view layout of the demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 29. STEVAL-ISQ002V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 30. Pin description of RS232 D9 connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

2

C initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Doc ID 13286 Rev 2 5/43

PMBus introduction AN2511

1 PMBus introduction

1.1 PMBus protocol description

The PMBus protocol is intended to cover a wide range of power system architectures and
converters.

PMBus devices must use the system management bus (SMBus), version 1.1. Implemented
over the industry-standard SMBus serial interface, the PMBus protocol facilitates the
programming, control and real-time monitoring of compliant power conversion products.

1.1.1 SMBus version 1.1

The system management bus (SMBus) is a two-wire interface through which various system
component chips can communicate with each other and with the rest of the system. It is
based on the principles of operation of I

For more information about SMBus, refer to AN1713, available from www.st.com.

1.1.2 Extensions to SMBus version 1.1 specification

1. Block write-block-read process call

To support certain commands of the PMBus command language, PMBus devices must
support the "Block write-block-read process call" described in Section 5.5.8 of Version

2.0 of the SMBus Specification.

2. Host notify protocol

PMBus devices may support the host notify protocol described in Section 5.5.9 of
Version 2.0 of the SMBus Specification. If a PMBus device supports the host notify
protocol, the two data bytes sent to the host are the same as the data bytes returned by
the STATUS_WORD command.

3. Group command protocol

PMBus devices must support the group command protocol. The group command
protocol is used to send commands to more than one PMBus device. The commands
are received in one transmission. When the devices detect the STOP condition that
ends the command, they all begin executing the command they received.

4. Addressing

PMBus devices use seven bit addresses.

5. Packet error checking (PEC)

Support for the SMBus packet error checking (PEC) protocol is optional.

2

C.

1.2 Hardwired signals

1.2.1 Electrical interface

The following diagram shows the interface between different PMBus devices. ST72264G1 is
the selected microcontroller, which has a multi-master I
acts as PMBus master. It communicates with any compatible PMBus slave using a 4-pin
interface. SMBC is the clock from the master. SMBD is the data pin. Both SMBC and SMBD
should be pulled up with a 4.7 kΩ resistor. SMBALERT is the SMBus alert pin, which helps

6/43 Doc ID 13286 Rev 2

2

C interface. This microcontroller

AN2511 PMBus introduction

the slave to alert the master whenever it wants to communicate. The control pin is used to
switch ON or OFF a PMBus slave.

Figure 1. Interface diagram

The CONTROL signal is an input signal on a power converter. It is used to turn the unit on
and off in conjunction with commands received via the serial bus. It can be configured as an
active high or active low signal through the ON_OFF_CONFIG command (refer to

Section 3.1).

This signal is optional but recommended.

1.2.2 Timing

No specific requirements are made when a PMBus device must respond to a state change
of a hardwired signal.

PMBus Master

(ST72F264G1)

SMBC (SCL)

SMBD (SDA)

SMBA (PA3)

CONTROL (PC0)

PMBus Slave

SMBC
SMBD

SMBA

CONTROL

Doc ID 13286 Rev 2 7/43

Implementation of PMBus using ST7 I2C AN2511

2 Implementation of PMBus using ST7 I2C

2.1 Firmware architecture

This section explains sequence of operation for different software modules.

2.1.1 I2C initialization

To use ST7 I2C for PMBus communication, the peripheral is initialized for 100 kHz
communication speed. The I

2

C is configured with an address of 0x30, as it can act as a

slave due to its multi-master capability. The following flowchart shows the sequence.

Figure 2. Flowchart: I

2

C initialization

Initialize I

OAR1 and OAR2 registers

Configure slave addresses

Enable I

acknowledge in I2CCR register

Set communication speed as

100kHz in I2CCCR register

START

2

C CR, CCR,

in OAR1 and OAR2

2

C peripheral and

STOP

The above flowchart is implemented in the function PMBus_Init.

2.1.2 Slave address and command code

The PMBus master addresses the slave with a 7-bit address. Once the slave device
acknowledges the address, the command code is sent corresponding to the PMBus
command and SMBus protocol (refer to Section 3.1).

Then, the microcontroller decodes the command code as shown in the following sequence.
Simultaneously, the SMBus_Mode variable is updated.

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AN2511 Implementation of PMBus using ST7 I2C

Figure 3. Flowchart: data length calculation

START

Check if command code equal

to Block protocol

No

Check if command code equal

to Byte protocol

Ye s

Ye s

Update

SMBus_Mode

for Block Command

Byte Count=1,

Update

SMBus_Mode

for Byte Command

Byte Count=6,

No

Byte Count=2,

Check if command code equal

to word protocol

No

Ye s

Update

SMBus_Mode

for Word Command

STOP

Inside both PMBus_CommandRead and PMBus_CommandWrite functions,
PMBus_DataLengthCalc is called which calculates the data length based on the

command code received.

2.1.3 Read and write operation

PMBus master performs read/ write operations with the slave device. Depending on the
command code, either PMBus_CommandRead or PMBus_CommandWrite is called. Inside
this function, the SMBus transaction type is selected as shown in the following sequence.

Figure 4. Flowchart: read operation

START

Check if SMBus_Mode for

Byte command

No

Check if SMBus_Mode for Word

command

No

Check if SMBus_Mode for

Send Block command

No

STOP

Ye s

SMBus Read byte protocol

1711811711811

S Slave Address Wr

Ye s

SMBus Read word protocol

171181171181

S Slave Address Wr

Ye s

SMBus Read block protocol

171181171181

S Slave Address Wr

A Command Code A S Slave Address Rd A Data Byte A P

A Comm and Code A S Slave Address Rd A Data Byte Low A ...

811

Data Byte High A P

A Com mand Code A Sr Slave Address Rd A Count Byte = 1 A ...

8181...811

Data Byte 1 A Data Byte 2 A ... Data Byte N A P

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Implementation of PMBus using ST7 I2C AN2511

Figure 5. Flowchart: write operation

START

Check if SMBus_Mode for

Send Byte command

No

Check if SMBus_Mode for Write

Byte command

Check if SMBus_Mode for Write

Word command

No

Check if SMBus_Mode for

Write Block command

No

STOP

Ye s

SMBus Send byte protocol

1711811

S Slave Address Wr

Ye s

SMBus Write byte protocol

171181811

S Slave Address Wr

Ye s

SMBus Write word protocol

17118181811

S Slave Address Wr

Ye s

SMBus Write block protocol

17118181181

S Slave Address Wr

A Data Byte AP

A Comma nd Code A Data Byte AP

A Comma nd Code A Data Byte Low A Dat a Byte HIgh A P

A Command Co de A Byte Count = N Rd A Data Byte 1 A ...

81...811

Data Byte 2

A ... Data Byte N AP

During the PMBus communication, if there are any errors in communication (acknowledge

2

failure, arbitration loss, bus error or SMBus timeout), the I

C peripheral is disabled. It is re-

initialized again inside the PMBus write/ read functions.

In case the SMBus Alert pin is pulled low by the slave to inform the master that it wants to
communicate, the slave address is programmed with the alert response address (0x18).
This is acknowledged by the slave that alerted the master. After the communication between
the master and slave is complete, the slave address is programmed with the user-defined
slave address. The default value of this user-defined address is 0x30.

In case of group operation, the write operation flowchart is followed without the stop
condition.

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AN2511 PMBus commands and source code

3 PMBus commands and source code

3.1 PMBus commands

The Part II - command language document of PMBus™ Power System Management
Protocol Specification v1.0 provides the list of PMBus commands. This driver supports the

following list of commands. For each command a table is given.

Table 1. Operation

Command name OPERATION

Command code 01h

The OPERATION command is used to turn the

Description

SMBus transaction type Read/ Write byte

Number of data bytes 1

Table 2. ON_OFF_CONFIG

Command name ON_OFF_CONFIG

Command code 02h

unit on and off in conjunction with the input from
the CONTROL (OUTEN) pin.

The ON_OFF_CONFIG command configures the

Description

combination of CONTROL (OUTEN) pin input
and serial bus commands needed to turn the unit
on and off.

SMBus transaction type Read/ Write byte

Number of data bytes 1

Table 3. CLEAR_FAULTS

Command name CLEAR_FAULTS

Command code 03h

Description

CLEAR_FAULTS is used to clear any fault bits
that have been set.

SMBus transaction type Send byte

Number of data bytes 0

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PMBus commands and source code AN2511

Table 4. RESTORE_DEFAULT_ALL

Command name RESTORE_DEFAULT_ALL

Command code 12h

The RESTORE_DEFAULT_ALL command
instructs the PMBus device to copy the entire
contents of the non-volatile default store memory

Description

SMBus transaction type Send byte

Number of data bytes 0

Table 5. STORE_USER_ALL

Command name STORE_USER_ALL

Command code 15h

Description

SMBus transaction type Send byte

to the matching locations in the operating
memory. Any items in default store that do not
have matching locations in the operating memory
are ignored.

The STORE_USER_ALL command instructs the
PMBus device to copy the entire contents of the
operating memory to the matching locations in
the non-volatile user store memory. Any items in
operating memory that do not have matching
locations in the user store are ignored.

Number of data bytes 0

Table 6. VOUT_MODE

Command name VOUT_MODE

Command code 20h

VOUT_MODE command, used for commanding
and reading output voltage, consists of a three bit

Description

mode (only linear format is supported.) and a
five-bit parameter representing the exponent
used in output voltage Read/Writes.

SMBus transaction type Read/ Write byte

Number of data bytes 1

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AN2511 PMBus commands and source code

Table 7. VOUT_COMMAND

Command name VOUT_COMMAND

Command code 21h

Description

SMBus transaction type Read/ Write word

Number of data bytes 2

Table 8. VOUT_MAX

Command name VOUT_MAX

Command code 24h

Description

SMBus transaction type Read/ Write word

Number of data bytes 2

Table 9. VOUT_MARGIN_HIGH

Command name VOUT_MARGIN_HIGH

Command code 25h

Description

VOUT_COMMAND is used to set the output
voltage, in volts (linear format).

The VOUT_ MAX command sets an upper limit
on the output voltage the unit can command
regardless of any other commands or
combinations.

This VOUT_MARGIN_HIGH command loads the
unit with the voltage to which the output is to be
changed when the OPERATION command is set
to "Margin High".

SMBus transaction type Read/ Write word

Number of data bytes 2

Table 10. VOUT_MARGIN_LOW

Command name VOUT_MARGIN_LOW

Command code 26h

This VOUT_MARGIN_LOW command loads the

Description

unit with the voltage to which the output is to be
changed when the OPERATION command is set
to "Margin Low".

SMBus transaction type Read/ Write word

Number of data bytes 2

Table 11. VOUT_OV_WARN_LIMIT

Command name VOUT_OV_WARN_LIMIT

Command code 42h

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