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 I2C peripheral for PMBus 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 I2C capability. This microcontroller acts 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 I2C peripheral, to support the standard PMBus commands. The results of this demonstration board interfaced with Artesyn's PMBus module are shown in this application note.

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

2/43	Doc ID 13286 Rev 2

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: I2C initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

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

Doc ID 13286 Rev 2

5/43

PMBus introduction	AN2511

1 PMBus introduction

1.1PMBus 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.

1.1.1SMBus 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 I2C.

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

1.1.2Extensions 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.

1.2Hardwired signals

1.2.1Electrical interface

The following diagram shows the interface between different PMBus devices. ST72264G1 is the selected microcontroller, which has a multi-master I2C interface. This microcontroller 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

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

PMBus Master

PMBus Slave

(ST72F264G1)

SMBC (SCL) SMBC

SMBD (SDA) SMBD

SMBA (PA3) SMBA

CONTROL (PC0) CONTROL

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.

1.2.2Timing

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

Doc ID 13286 Rev 2

7/43

Implementation of PMBus using ST7 I2C	AN2511

2 Implementation of PMBus using ST7 I2C

2.1Firmware architecture

This section explains sequence of operation for different software modules.

2.1.1I2C initialization

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

START

Initialize I2C CR, CCR,

OAR1 and OAR2 registers

Configure slave addresses in OAR1 and OAR2

Enable I2C peripheral and acknowledge in I2CCR register

Set communication speed as 100kHz in I2CCCR register

STOP

The above flowchart is implemented in the function PMBus_Init.

2.1.2Slave 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.

8/43	Doc ID 13286 Rev 2

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

No

Check if command code equal

to word protocol

No

Byte Count=6, Yes Update

SMBus_Mode for Block Command

Byte Count=1, Yes Update

SMBus_Mode for Byte Command

Byte Count=2, Yes 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.

2.1.3Read 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

Yes

SMBus Read byte protocol

1	7	1	1	8	1	1	7	1	1	8	1	1
S	Slave Address	Wr	A	Command Code	A	S	Slave Address	Rd	A	Data Byte	A	P

No

Check if SMBus_Mode for Word command

Yes

SMBus Read word protocol

1	7	1	1	8	1	1	7	1	1	8	1
S	Slave Address	Wr	A	Command Code	A	S	Slave Address	Rd	A	Data Byte Low	A	...

	No											8						1	1
													Data Byte High					A	P
Check if SMBus_Mode for				Yes
					SMBus Read block protocol
Send Block command
		1			7		1	1	8			1			1				7		1		1			8			1
	No	S		Slave Address			Wr	A	Command Code					A	Sr			Slave Address				Rd	A			Count Byte = 1			A	...
STOP
							8		1			8			1			...			8			1		1
						Data Byte 1				A		Data Byte 2					A	...	Data Byte N						A		P

Doc ID 13286 Rev 2

9/43

Implementation of PMBus using ST7 I2C	AN2511

Figure 5. Flowchart: write operation

START
Check if SMBus_Mode for		Yes	SMBus Send byte protocol
Send Byte command
	1		7	1	1	8		1	1
	S	Slave Address		Wr	A	Data Byte		A	P
No
Check if SMBus_Mode for Write		Yes	SMBus Write byte protocol
Byte command
	1		7	1	1	8		1		8		1	1
	S	Slave Address		Wr	A	Command Code		A		Data Byte		A	P
Check if SMBus_Mode for Write		Yes	SMBus Write word protocol
Word command	1		7	1	1	8		1		8		1		8	1	1
	S	Slave Address		Wr	A	Command Code		A	Data Byte Low			A	Data Byte HIgh		A	P
No
Check if SMBus_Mode for		Yes	SMBus Write block protocol
Write Block command
	1		7	1	1	8		1		8		1	1	8		1
No	S	Slave Address		Wr	A	Command Code		A	Byte Count = N			Rd	A	Data Byte 1		A ...
STOP
				8		1 ...		8		1	1
			Data Byte 2			A ...	Data Byte N			A	P

During the PMBus communication, if there are any errors in communication (acknowledge failure, arbitration loss, bus error or SMBus timeout), the I2C peripheral is disabled. It is reinitialized 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.

10/43

Doc ID 13286 Rev 2

AN2511	PMBus commands and source code

3 PMBus commands and source code

3.1PMBus 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		unit on and off in conjunction with the input from
		the CONTROL (OUTEN) pin.
SMBus transaction type		Read/ Write byte
Number of data bytes		1

Table 2.	ON_OFF_CONFIG
Command name		ON_OFF_CONFIG
Command code		02h
		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

Doc ID 13286 Rev 2

11/43

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		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.
	SMBus transaction type		Send byte
	Number of data bytes		0
	Table 5.	STORE_USER_ALL
	Command name		STORE_USER_ALL
	Command code		15h
			The STORE_USER_ALL command instructs the
			PMBus device to copy the entire contents of the
	Description		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.
	SMBus transaction type		Send byte
	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

12/43

Doc ID 13286 Rev 2

AN2511			PMBus commands and source code
	Table 7.	VOUT_COMMAND
	Command name		VOUT_COMMAND
	Command code		21h
	Description		VOUT_COMMAND is used to set the output
			voltage, in volts (linear format).
	SMBus transaction type		Read/ Write word
	Number of data bytes		2
	Table 8.	VOUT_MAX
	Command name		VOUT_MAX
	Command code		24h
			The VOUT_ MAX command sets an upper limit
	Description		on the output voltage the unit can command
			regardless of any other commands or
			combinations.
	SMBus transaction type		Read/ Write word
	Number of data bytes		2
	Table 9.	VOUT_MARGIN_HIGH
	Command name		VOUT_MARGIN_HIGH
	Command code		25h
			This VOUT_MARGIN_HIGH command loads the
	Description		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

Doc ID 13286 Rev 2

13/43