PMBus Implementation Using the MSP430 USCI
Contents
1. Decide Protocol of Issued Command PC Function Call PC Access Level Transmit Command Byte Read Back Data From Slave Figure 6 Software Architecture The application level contains the PMBus function calls and the user issued commands that are passed as arguments The PMBus level processes the commands it receives from the application level Note that all PMBus commands are defined by two parameters the Protocol Format and the Command Code The Protocol Format parameter defines the 1 C action that needs to be performed to execute the command as explained in Section 2 2 For example Read Word format indicates that one byte is transmitted and two bytes are received The Command Code parameter is the hexadecimal byte that indicates which command should be executed For example the command to read the input voltage is 0x88 The summary of command codes in the form of hex bytes can be found in the PMBus Specification Part Il Appendix I 3 The PMBus function decides to which of the defined Protocol Formats the command belongs and the associated Command Code All 126 PMBus commands defined in the standard except user defined commands have been classified under the previously mentioned formats sorted in a header file to lessen overhead Based on the Protocol Format decision the I C functions are called and the Command Code is transmitted The PMBus function also implements PEC as an added feature for optional use Users who need P2. This layer also implements a timeout capability using Timer A The timeout feature is added to ensure that slower slave devices do not hold the clock for any more than trmeoutmax 35 ms If the timer expires the timer ISR resets the USCI module and exits low power mode A port pin P5 1 connected to LED on target board is turned high and a flag is set to indicate that timeout has occurred The user can add further timeout handling capabilities as needed Sourcing Timer A from ACLK 32 kHz crystal allows the MSP430 to be in LPM3 for maximum power savings For more details on using the USCI module as an 1 C master device see the application report Using the USCI PC Master 4 4 Example Application Using the UCD9112 Synchronous Buck Controller Slave The UCD9112 buck controller device is a part of the UCD911x family of digital power controllers This family of controllers provides PMBus support including support for features such as the alert response control signal and PEC The device was chosen because it can be configured easily and supports almost all major PMBus commands The demonstration application uses the UCD9112 Dual Phase Synchronous Buck Digital Controller Evaluation Module UCD9112 EVM which provides convenient test points and output headers for PMBus lines 10 A list of compatible commands and data format details are provided in the document PMBus Support in UCD91 1x Family of Digital Power Controllers 5 Figure 7 shows the elec
3. PC Layer Data Control Alert Figure 1 Communication Model PMBus Layer The following significant features uniquely identify the PMBus protocol and establish its position as a valuable part of any power management system Alert Signal SMBALERT The SMBALERT line is used by slave devices to notify the master in the presence of a system fault This line is a wired AND signal and is tied high at reset similar to I 7C clock and data lines The slave device can pull it low at any time to notify the host microcontroller that it needs to communicate When the master PMBus device receives an alert from the slave the master can be configured to read the status registers of the slave device to determine the type and location of the fault Once the fault has been read and recorded the slave device can be notified and its status registers reinitialized In systems that have multiple slaves tied to the bus the master uses the Alert Response Address ARA to determine which slave pulled the alert line low If multiple slaves are asserting the alert simultaneously the slave with the lowest address wins This application report however deals with alert response implementation for single slave only for multi slave implementation with the alert response see System Management Bus SMBus Specification V2 0 1 Control Signal CONTROL On off control of the slave device is achieved by using the control line in combination with comman
4. can be used to enable or disable a certain feature in the slave device A graphical representation of the Send Byte format is shown in Figure 2 7 1 1 8 1 1 1 fe Slave Address Pw a Command Byte pa P S Start P Stop Sr Repeated Start W Write R Read A Master ACK A Slave ACK Figure 2 Send Byte Protocol 2 2 2 Read Byte This format is used to read a single byte of information from the slave device The I C action for this format is to transmit one byte and receive one byte For example the master can issue a STATUS_ BYTE command to read the lower byte of the slave device s status register This is followed by a repeated start condition that indicates a direction change from write to read The slave device stops transmitting on receiving a STOP or a NACK from the master In this case only one data byte is transmitted by the slave before it gets a STOP This format differs from the Read Write Byte format see Section 2 2 5 in that Read Byte commands are typically addressed to registers or parameters that are read only they cannot be modified A graphical representation of the Read Byte format is shown in Figure 3 1 7 1 1 8 1 1 7 1 1 8 1 1 g Hi jii pg ai B iii dadia HO dita oe e afa Figure 3 Read Byte Protocol 2 2 3 Write Byte This format is used to write a single byte of information to the slave device The 1 C action for this format is to transmit two bytes This format starts with transmitting the command code f
5. module in I C mode It is called once through the PMBus initialization subroutine The following parameters are passed as arguments to this function Name Description Slave_Address Device address of the slave Prescale This parameter is used to compute the desired baud rate It is computed as the quotient of DCO frequency when divided by the prescale parameter The USCI I C clock is configured to operate at 58 kHz default DCO frequency 18 using this function TI_USCI_I2C_Slave_ Present Slave_Address This function detects the presence of a slave The following parameter is passed as an argument to this function Name Description Slave_Address Device address of the slave The return value is the result of the operation The function returns a zero if the slave is present and has acknowledged and a non zero value if the slave is absent or not ready to acknowledge This function also can be used to poll slave devices that are slow in responding to the master If there are no slave devices connected to the bus then the master device is trapped in a while loop and the LED is toggled rapidly until the issue is resolved TI_USCIL_12C_NotReady This function takes no parameters and returns zero if the I C bus is not busy If the I 7C bus is busy then it returns a value different from zero It can be used to poll the C lines to indicate the status of an ongoing transaction SLAA386A Januar
6. provides the specified output only when the control line is high and the OPERATION command instructs the output unit to be turned on Care should be taken to avoid changing device parameters by writing to registers while the device is in operation If a system fault occurs the slave device pulls the alert line low and records the source of the fault in the status register The status register can be read and the CLEAR_FAULTS command can be sent to inform the slave device that the master has acknowledged the fault On clearing the fault or if the fault condition no longer exists the alert line is released The slave device also provides PEC functionality and can generate validate PEC bytes as needed These key features are illustrated using demonstration application code as explained in Section 6 PMBus Implementation Using the MSP430 USCI SLAA386A January 2008 Revised February 2008 Submit Documentation Feedback Wy TEXAS INSTRUMENTS www ti com Function Description 5 Function Description 5 1 This section is divided into two subsections based on the software level the functions service USCI FC Interface Functions The USCI I C functions are derived from those used in Using the USCI C Master 4 These functions are collectively available through the file 2Cfunctionset c The function prototypes are declared in the header file Tl USCI_I2C_master h TI_USCIL_12C_Init Slave_Address Prescale This function initializes the USCI
7. relay data representing commands control and information over a serial bus 3 In addition to the data and clock lines provided by I C the PMBus protocol implements the optional alert response for host notification in the presence of a fault and control line for turning the slave device on off The PMBus command layer provides a set of 256 commands that the host microcontroller can use to instruct slave PMBus devices Note PMBus commands and their functionality as mentioned in this application report can be found in PMBus Specification Part Il Appendix 1 3 The PMBus protocol also implements a timeout feature present in SMBus that prevents slower slave devices from holding the clock line for longer than the specified timeout interval This limits the minimum allowable frequency of IC transactions to 10 kHz similar to SMBus but absent in 1 C For further differences in timing and DC specifications between the protocols see System Management Bus SMBus Specification V2 0 1 A new feature that increases reliability and robustness of this protocol is Packet Error Checking PEC PEC was first introduced in version 1 1 of the SMBus protocol and is implemented by using a Cyclic Redundancy Check 8 CRC 8 algorithm to validate the integrity of a transaction It should be noted that PMBus can function as a 2 wire protocol The data and clock lines are retained from the IC protocol for transmitting receiving data and for controlling the cl
8. EC implementation in the host microcontroller can select the appropriate file that allows for PEC capabilities Generating the PEC byte involves invoking the CRC 8 algorithm provided in a function The CRC function performs an XOR operation on the input data stream with the CRC 8 polynomial C x x8 x x 1 This calculation is done in the order bits are received and also can be considered a brute force polynomial division technique The algorithm used to calculate the CRC byte is modified from the application report CRC Implementation With the MSP430 2 PMBus master devices that implement PEC have either prior knowledge of whether or not the slave supports the feature or they are expected to determine this by reading information from the slave The master transmitter generates the PEC byte and inserts it at the end of the transmit data stream If the PEC byte is not acknowledged by the slave then the transaction is considered invalid PMBus Implementation Using the MSP430 USCI SLAA386A January 2008 Revised February 2008 Submit Documentation Feedback Wy TEXAS INSTRUMENTS www ti com Example Application Using the UCD9112 Synchronous Buck Controller Slave If the master is receiving then it generates the extra clock cycles needed to receive the PEC byte from the slave as the last byte of the transaction Master receivers can then check the validity of the PEC byte by generating their own PEC and comparing it to the one received from t
9. IR 0x02 PMBusInit 0x08 Initialize PMBus device Operation_Result PMBus_PEC READ_VIN 0 0 Vin Read input voltage if Operation_Result 1 PEC byte valid while 1 P50UT 0x02 Toggle LED for i 0 i lt 0x4000 i SW Delay while 1 Trap CPU 7 Code Size Table 2 shows the code size for the included examples The code was complied using IAR Embedded Workbench KickStart for MSP430 V 4 09A with low optimization settings Table 2 Code Size IAR Files Code Size Bytes I2CFUNCTIONSET C 470 PMBUSFN C 478 PMBUS_PECFN C 900 API FILES 80 8 References System Management Bus SMBus Specification V2 0 www smbus org CRC Implementation With the MSP430 SLAA221 Power Management Bus PMBus Specification Part and ll Version 1 1 www pmbus org Using the USCI FC Master SLAA382 PMBus Support in UCD911x Family of Digital Power Controllers SLUA427 UCD9112 Digital Dual Phase Synchronous Buck Controller data sheet SLVS711 FC Bus Specification and User Manual NXP Semiconductors 2007 http Avww nxp com acrobat usermanuals UM10204_3 pdf 8 MSP430x4xx Family User s Guide SLAU056 9 MSP430xG461x data sheet SLAS508 10 UCD9112 Dual Phase Synchronous Buck Digital Controller Evaluation Module SLUU295 NOOO PRON gt SLAA386A January 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI 15 Submit Documentation Feedbac
10. LIMIT can be used as a Read Word to read the default value or Write Word to configure the new value command When used as a Read Word command RWFlag 1 and when used as a Write Word command RWFlag 0 For all other protocol formats this parameter is don t care and is passed as zero Message This parameter is defined only for Write Byte or Write Word commands It contains the data byte or word that is to be written to the slave device Because the parameter is of type unsigned int a byte or a word may be passed If a data word is passed it is unpacked and stored in the transmit buffer as two bytes as C operations are performed byte wise If the byte or word is an illegal value the UCD9112 device does not acknowledge it NACK 5 Received_Value This parameter is a pointer to an array that holds the received values passed by the I C function It is used only if any bytes or words are to be received from the slave device For transmit only operations this parameter is a don t care and is passed as zero The PMBus function returns the status of the 1 C transaction A successful transaction returns a zero and a NACK is represented by a one PMBus_PEC Command_Byte RW_Flag Message Received_Value This function is defined in the file PMBus_PECfn c Its structure is almost identical to the PMBus function However it has the additional ability to generate the PEC byte if the master is a transmitter or if th
11. and control functionality Also the USCI_Init function is called to initialize the USCI module This function checks for the presence of a slave device using the USCI_Slave_Present function that is repeatedly called in a while loop until the slave device acknowledges the address Also if there are no slave devices connected to the bus then the master device is trapped in a while loop and the LED is toggled rapidly until the issue is resolved The following parameter is passed as an argument to this function Name Description Device_Address Device address of the slave PMBus Implementation Using the MSP430 USCI SLAA386A January 2008 Revised February 2008 Submit Documentation Feedback WB TEXAS INSTRUMENTS www ti com 5 2 2 5 2 3 Function Description PMBus Command_Byte RW_Flag Message Received_Value This function implements the PMBus software stack that is used to control the hardware access or 1 C layer It includes the necessary functionality to determine the Protocol Format and the Command Code of the PMBus command passed from the application level The Command Code is determined using a lookup table defined in the variable list_of_commands The look up table sorts the PMBus commands by the order of the Protocol Format they belong to For example all Read Byte commands are allocated to the first Protocol Format Once the Protocol Format is determined switch case logic is used to call the 1 C functions t
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13. ds on the bus The control line is configured as active high or active low based on the ON_OFF_CONFIG command The OPERATION command can then be used to turn the slave device on off through software Packet Error Checking PEC PEC is optionally implemented in PMBus devices but is highly recommended due to the critical nature of data validity in power management systems Packet Error Code also PEC bytes are generated using the popular CRC 8 algorithm that is based on performing XOR operations on the input bit stream with a fixed CRC polynomial The PEC byte is calculated on all bytes in the I C transaction including device address and read write PEC does not include start stop ACK NACK and repeated start bits SLAA386A January 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI 3 Submit Documentation Feedback 3 TEXAS INSTRUMENTS www ti com PMBus Protocol 2 2 PMBus Protocol Formats To understand implementation of PMBus commands and their classification a brief overview of PMBus protocol formats is needed All PMBus commands defined in the standard can be classified under one of the formats in the following sections 1 2 2 1 Send Byte This format is typically used to instruct the slave device to perform a specified action The IC action for this format is to transmit one byte For example the CLEAR_FAULTS command instructs the slave device to clear all faults and reinitialize fault registers This format also
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15. e This function is a modified version of the CRC16 CRC32 functions used in CRC Implementation with the MSP430 2 It is defined in the file PMBus_PECfn c and is used only by the function PMBus_PEC to generate the PEC byte The standard definitions used by this function are listed in the header file PMBUS_PEC h The following parameters are passed as arguments to this function Name Description CRC Initial value of the CRC byte Poly CRC 8 polynomial 0x07 the 1 in the polynomial 0x107 is implied 2 Pmsg Input bit stream for which the PEC byte needs to be calculated All bytes in the transaction including Address and R W bits are used Start Stop and ACK NACK bits are not used Msg_Size Number of bytes in the input bit stream This function returns the calculated CRC byte Application Examples The included application examples illustrate the key features of the PMBus protocol as described in Section 2 2 General PMBus Status Polling This application file checks for presence of slave device and reads parameters such as input voltage output voltage and switching frequency from the UCD9112 slave device The files that must be included in a project are e 2Cfunctionset c e PMBusfn c e Status Poll c Also the header files PMBUS h and Tl_USCI_l2C_master h must be accessible by the project Example code that illustrates how device parameters are retrieved from the slave device is shown in the fo
16. e Functions cece eee eee ee ee ee eee ee eeeeeeeeeneeeneeeeeeeeneenens 10 6 Application ExaMpleSisaveceivcnavewenevicwnienanncweb ester a E 12 6 1 General PMBus Status Polling ccceceeeeeee cece seen neces eeeeeeeeeeeeeeneeees 12 6 2 Alert Line Implementation ccccceeeeeeee eens ee eeee snes eeeeeeeeeeeneeeeneeeneeeees 13 6 3 Control Line Implementation c cceeeeeeeeeee eee eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 14 6 4 Packet Error Check Implementation cceeceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeneees 15 7 CGOde SIZO ar anaa a AA EE E E RE 15 8 References inachi EEE a E EE 15 Appendix A Associated Files cccceeeee eee reece neeee seen eneeeeneeeeeeeeeneeeneeeenneeeneeennes 16 1 Communication Model sisser sessin a EE EEEE Ea 3 2 Send Byte ProtOCol sssse sss ae e a e E E 4 3 Read Byte Protocolsosissrene rinan EEEE EEE EEEE 4 4 Write Byte Protocol sits as iv ax everatevususvever av atexanaxumuy ey EEEE EEEN ie 4 5 Read Word Proto hives ci ieee sete siccid cians naan and wa niesian cians aa dees Ea 5 6 Software Architectures coc hivvcscccs cetera ienien iai cade veduosteueaeueas 6 7 MSP430 PMBus Interface to UCD9112 ccccccc esse cece eeeeeeeeeeeeeeeeeeaeeeenesaneees 8 List of Tables 1 Differences Between I C SMBus and PMBuS Protocols esecsceeceeececeeeeeeeerereus 2 2 Gode Size AR sass senrecmiiccanticaneicienicomdinacnty tua E EO ETS 15 All trademarks are the property of their respective owner
17. e master can check the validity of the received PEC byte if the master is a receiver The PEC byte is generated either for transmission or for comparison and validation using the function crc8MakeBitwise This function is a modified version of the CRC16 CRC32 functions defined in CRC Implementation with the MSP430 2 For the master transmitter once the PEC byte is generated it is placed as the last value in the transmit buffer If the slave device acknowledges this last byte then data integrity is said to have been maintained else the slave does not acknowledge NACK the PEC byte This can be verified by checking the Ack_Status variable For the master receiver the last value in the receive buffer is considered to be the PEC byte stored in the variable crc_slave_generated A PEC byte is then generated on the master side in variable crc_master_generated and the two bytes are compared If the bytes are found equal the 1 C data is considered valid The arguments passed to this function are the same as those for the PMBus function The function has one return value that reflects the PEC status of the transaction If the PEC status is pass a one is returned otherwise a zero is returned SLAA386A January 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI 11 Submit Documentation Feedback Wy TEXAS INSTRUMENTS www ti com Application Examples 5 2 4 6 1 12 crc8MakeBitwise CRC Poly Pmsg Msg_ Siz
18. figuring MSP430 Modules The demonstration application presented in the accompanying code see Section 4 uses an MSP430FG461x device with the MSP TS430PZ100 target board As mentioned earlier the PMBus uses a 4 wire interface The USCI module configured in I C mode furnishes the clock and the data lines Any port pin can be used for the alert response line It is tied high using pullup resistors similar to clock and data lines and triggers an interrupt on a high low transition i e whenever the slave pulls the line low due to a system fault The control line is also an I O pin configured as an MSP430 output line This line is used in combination with commands on the serial bus to turn the slave device on and off SLAA386A January 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI 5 Submit Documentation Feedback 3 TEXAS INSTRUMENTS www ti com PMBus and MSP430 3 2 Software Implementation The software for this application is implemented in three levels as shown in Figure 6 The I C access level and the PMBus level are independent of the slave device The application level is specific to the slave device being used and consists of an initialization routine call followed by PMBus function calls The demonstration package included can therefore be used with any PMBus compatible slave device with minor changes in the application level Application Level Initialize PMBus Master PMBus Function Call PMBus Level
19. hat are needed to implement the command For example if the READ_VIN command is passed from the application level the PMBus function determines the Command Code 0x88 needed to process this command and the Protocol Format it belongs to Read Word The function then proceeds to call the 2C transmit operation and to pass all the parameters needed for the transaction In case of Write Byte Word commands the bytes to be written to the slave device are processed and presented as a part of the transmit buffer to the USCI module The function also sets the master device in LPMO when I C transactions are being carried out If a receive operation has been performed the function returns the received data bytes through a pointer to the application level The following parameters are passed as arguments to this function Name Description Command_Byte This is the actual PMBus command as passed by the user e g READ_VIN It corresponds to an index value in the PMBus lookup table It is used to determine the Protocol Format and the Command Code of the specified PMBus command A list of allowed PMBus commands can be found in Power Management Bus PMBus Specification Part and II 3 and those compatible with the UCD9112 device can be found in PMBus Support in UCD911x Family of Digital Power Controllers 5 RWFlag This parameter is used only if the user command belongs to Read Write Byte or Read Write Word protocol format For example VIN OV_WARN_
20. he Read Write Byte format typically address slave device parameters that can be either written to or read from The I C action for this format changes according to direction of data flow see Figure 3 and Figure 4 For example the command VIN_OV_WARN_LIMIT sets the threshold for overvoltage fault in a device and this threshold value may be preserved in a register The register can be read from to view the default threshold value or written to to configure a new threshold value depending on what the user needs Read Write Word Commands that use the Read Write Word format are similar in purpose and format to Read Write Byte except that two bytes can be read from or written to a slave device in any transaction PMBus devices receive or transmit data bytes in two formats DIRECT and LINEAR Any given device is capable of supporting only one of these formats 3 Implementation of data post processing based on these two formats has not been done in the accompanying code and is beyond the scope of this application report PMBus and MSP430 This section has been divided into two subsections for ease of understanding The first section deals with configuring the MSP430 USCI module and I O pins for alert response and control line implementation 8 The second section deals with the software architecture and the implementation of PMBus commands using the MSP430 It is also an overview of how the PMBus layer interacts with the hardware layer Con
21. he slave device PMBus slave devices that implement PEC must be able to respond to master devices with or without PEC support Slave transmitters must have the capability of generating PEC bytes and inserting them as the final byte of any transaction if requested Slave receivers must be able to accept the PEC byte check to see if the byte is valid or not and respond with an ACK NACK accordingly 1 The PMBus layer also supports alert response and control functionality by configuring two I O pins for the SMBALERT and CONTROL signals The SMBALERT line is configured to trigger an interrupt on high low transitions The port ISR services the interrupt and returns to the application level for further processing Implementing alert response functionality using the port ISR ensures better system efficiency as it eliminates the need for polling The CONTROL line is configured as active high but needs the OPERATION command to turn the device on Consequently the port pin configured for use as the control line is driven high in the PMBus initialization routine The IC access level consists of an initialization routine that configures the USCI in IC mode and the functions needed to perform I7C transactions C functions are used to check if the slave device is present verify if the bus is free or send and receive one to n bytes based on commands from the PMBus layer All IC functions are executed in low power mode 0 LPMO and are optimized to work using ISRs
22. ication example void main void volatile unsigned int i WDTCTL WDTPW WDTHOLD Stop WDT PMBusInit 0x08 Initialize PMBus device PMBus READ_VIN 0 0 Vin Read initial Vin lt 13 20V PMBus STATUS_WORD 0 0 Status Read initial status no faults PMBus CLEAR_FAULTS 0 0 0 Clear any existing faults PMBus VIN_OV_WARN_LIMIT 1 0 Over_Voltage Read Vin threshold value 13 20V while 1 __bis_SR_register LPMO_bits GIE Enter LPM PMBus STATUS_WORD 0 0 Status_Fault Read status fault indicated for i 0 i lt 0x7FFF i SW Delay for Vin to settle PLACE BREAKPOINT HERE Remove fault condition Vin lt 13 2V PMBus CLEAR_FAULTS 0 0 0 Clear all faults P50UT 0 LED off P1IE BIT4 P1 4 Alert Interrupt enabled Note An alert condition is repeatedly generated as long as the fault exists Therefore while creating the fault condition maintaining the voltage above the warning threshold for long periods may result in multiple or nested alerts SLAA386A January 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI 13 Submit Documentation Feedback 3 TEXAS INSTRUMENTS www ti com Application Examples 6 3 14 Control Line Implementation This application demonstrates the use of the control line to turn the slave device on or off The control line functionality is typically configured using the ON_OFF_CONFIG co
23. k 3 TEXAS INSTRUMENTS www ti com Appendix A Appendix A Associated Files The following files are included in the associated zip package Folder Without PEC e 2Cfunctionset c USCI 12C functions e PMBusfn c PMBus functions without PEC implementation e PMBUS h Definitions needed by PMBus files e TI_USCI_l2C_master h Definitions needed by the file I2Cfunctionset c e Status _Poll c General PMBus device parameter read e Alert_Notify c PMBus Alert functionality example e ON_OFF_Control c PMBus Control functionality example Folder Il With PEC e 2Cfunctionset c USCI 12C functions e PMBus_PECfn c PMBus functions with PEC implementation e PMBUS_PEC h Definitions needed by PMBus files e TI_USCI_l2C_master h Definitions needed by the file I2Cfunctionset c e PEC_Check c General parameter read with PEC SLAA386A January 2008 Revised February 2008 Submit Documentation Feedback IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries Tl reserve the right to make corrections modifications enhancements improvements and other changes to its products and services at any time and to discontinue any product or service without notice Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete All products are sold subject to Tl s terms and conditions of sale supplied at the time of or
24. ki TEXAS Application Report INSTRUMENTS SLAA386A January 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI Priya Thanigai MSP430 Applications ABSTRACT This document provides an example application for the Power Management Bus PMBus protocol implementation using the MSP430 as a master PMBus device The PMBus protocol is an open standard power management protocol used for communicating with power conversion devices It is implemented using the popular 1 C communication protocol at a hardware level and is controlled by a software interface of PMBus commands The demonstration application has been created for use with the MSP430 USCI module configured in I7C mode The code is intended for single master slave applications only Contents 1 INtOCGUCTION oc e cece eect eee een eee eee ee en eee E E EE ES 2 2 PMBUS Protocol si cieinicemasnienean a EE 2 2 1 PMBUS Layef isoine E E 3 2 2 PMBus Protocol Formats ccscceeeeeeeeeeeeeeeeneeeeeeeeeeeeeeneeeeeeeeneeeeneeennes 4 3 PMBUS and MSP480 ssendu a a nnd enabicatsnceitemewemens 5 3 1 Configuring MSP430 Modules sssaaaaannnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn 5 3 2 Software Implementatio Mesenas EES 6 4 Example Application Using the UCD9112 Synchronous Buck Controller Slave 7 5 FUNCTION Description ciiescinccvenanananie cna danaa m aE 9 5 1 USCI IC Interface Functions cccceeeeceeceeceeceeceseaeceeceeeaesueserseesensaes 9 5 2 PMBus Interfac
25. llowing code void main void WDTCTL WDTPW WDTHOLD Stop WDT PMBusInit 0x08 Initialize PMBus device PMBus CAPABILITY 0 0 Capbl1 Read device capability PMBus READ_VIN 0 0 Vin Read input voltage PMBus READ_VOUT 0 0 Vout Read output voltage PMBus READ_FREQUENCY 0 0 Freq Read switching frequency while 1 Trap CPU PMBus Implementation Using the MSP430 USCI SLAA386A January 2008 Revised February 2008 Submit Documentation Feedback WB TEXAS INSTRUMENTS 6 2 www ti com Application Examples Alert Line Implementation This application illustrates one way the alert functionality can be implemented The initial device parameters are read after which the master device is put to sleep When the user increases the input voltage beyond the overvoltage warning threshold default value for the UCD9112 device is 13 20 V a system fault occurs This causes the alert line to be pulled low and the port ISR to wake up the PMBus master device The master device then proceeds to service the fault by reading the status registers and sending the CLEAR_FAULTS command over the serial bus Once the fault has been serviced the master device returns to LPMO The files that must be included in a project are e 2Cfunctionset c e PMBusfn c e Alert_Notify c Also the header files PMBUS h and TI_USCI_I2C_master h must be accessible by the project The following code illustrates this appl
26. mmand The data byte 0x1E is written using this command This is the default device setting 5 It indicates that the UCD9112 device is configured to have an active high control line and that it also needs the OPERATION command to turn on or off the output Initially the OPERATION command is used to turn the output off At this time reading the output voltage returns a result of 0 V 0x0044 Then the VOUT_COMMAND instruction is used to configure the output voltage to 1 V default value 0x080D The OPERATION command turns the device on Now when the output voltage is read back it is shown to be the previously set value of 1 V 0x0800 This application thus illustrates how to turn the slave device output on or off using software commands Note that the device has a specified rise and fall time time taken for the output unit to turn on or off If the Vout parameter is read before this specified time it may reflect an incorrect value A small delay has been added in the example code to prevent this The files that must be included in a project are e 2Cfunctionset c e PMBusfn c e ON_OFF_Control c Also the header files PMBUS h and Tl_USCI_Il2C_master h must be accessible by the project The following code illustrates this application example void main void WDTCTL WDTPW WDTHOLD Stop WDT PMBusInit 0x08 Initialize PMBus device PMBus ON_OFF_CONFIG 0 0x1E 0 Active high OPERATION c
27. ocking of data respectively The alert response and control signals are optional implementations enhancements for host microcontrollers that are willing to trade two GPIO pins for the ability to service a system fault and to turn the slave device on or off using software Table 1 briefly lists the significant differences between these protocols Table 1 Differences Between I C SMBus and PMBus Protocols Protocol Alert Response Control Line Maximum Timeout cui PEC PC No No No 0 DC No SMBus Yes No 35 ms 10 kHz Yes PMBus Yes Yes 35 ms 10 kHz Yes Figure 1 shows the architecture of the PMBus host microcontroller s communication model The application layer is at the user interaction level and also can be viewed as a data translation interpretation layer It performs application services and issues requests to the PMBus layer The PMBus layer accepts commands from the application layer It processes these commands and instructs the hardware access I C layer on how to execute them The IC layer in conjunction with the alert response and control line provides the physical interface needed for direct communication with the slave device PMBus Implementation Using the MSP430 USCI SLAA386A January 2008 Revised February 2008 Submit Documentation Feedback Wy TEXAS INSTRUMENTS www ti com 2 1 PMBus Protocol PMBus Master Device Application Layer PMBus Layer Clock PMBus Slave Device
28. ollowed by a repeated start and then the data that is to be written to the slave device For example using the STORE_DEFAULT_CODE command the master can instruct the slave device to store the parameter matching the command code in the data byte from the operating memory to the nonvolatile default store memory A graphical representation of the Write Byte format is shown in Figure 4 This format differs from the Read Write Byte format see Section 2 2 5 in that Write Byte commands are typically addressed to registers or parameters that are write only they cannot be read back Note that there are no PMBus commands that are Write Word only 1 7 1 1 8 1 1 7 1 1 8 1 1 8 Slave Address gg Command Byte as Slave Address gg Write Data Byte B Figure 4 Write Byte Protocol 4 PMBus Implementation Using the MSP430 USCI SLAA386A January 2008 Revised February 2008 Submit Documentation Feedback Wy TEXAS INSTRUMENTS www ti com 2 2 4 PMBus and MSP430 Read Word This format is similar to the Read Byte format except that two data bytes are read from the slave device The C action for this format is to transmit one byte and receive two bytes A graphical representation of the Read Word format is shown in Figure 5 1 7 1 1 8 1 1 7 1 1 8 1 g Slave Address wa Command Byte D Slave Address Ra Data Byte Low a eee 2 2 5 2 2 6 3 1 8 1 1 Data Byte High pa Figure 5 Read Word Protocol Read Write Byte Commands that use t
29. ommand PMBus OPERATION 0 0x00 0 Turn Unit Off o p 0V PMBus OPERATION 1 0 Oprn Read back oprn status for i 0 1 lt 2000 i Delay for Vout to settle PMBus READ_VIN 0 0 Vin Read Vin PMBus READ_VOUT 0 0 Vout Read Vout 0V PMBus VOUT_COMMAND 0 0x080D 0 Configure output voltage 1V PMBus OPERATION 0 0x80 0 Turn Unit On Margin off for i 0 1 lt 2000 i Delay for Vout to settle PMBus READ_VOUT 0 0 Vout Read Vout 1V PMBus OPERATION 0 0x00 0 Turn Unit Off o p 0V while 1 PMBus Implementation Using the MSP430 USCI SLAA386A January 2008 Revised February 2008 Submit Documentation Feedback Wy TEXAS INSTRUMENTS www ti com Code Size 6 4 Packet Error Check Implementation This application is a simple illustration of how PEC is implemented using the PMBus function A READ_VIN command is used to read three bytes of information the two bytes that represent the input voltage and the PEC byte If the PEC byte is found valid by the PMBus_PEC function the operation_result parameter holds a value of one otherwise it is zero A successful transaction valid PEC is indicated by toggling the LED The files that must be included in a project are e 2Cfunctionset c e PMBus_PECfn c e PEC_Check c Also the header files PMBUS_PEC h and TI_USCI_I2C_master h must be accessible by the project void main void WDTCTL WDTPW WDTHOLD Stop WDT P5D
30. ptical Networking www ti com opticalnetwork Microcontrollers microcontroller ti com Security www ti com security RFID www ti rfid com Telephony www ti com telephony RF IF and ZigBee Solutions www ti com Iprf Video amp Imaging www ti com video Wireless www ti com wireless Mailing Address Texas Instruments Post Office Box 655303 Dallas Texas 75265 Copyright 2008 Texas Instruments Incorporated
31. r of bytes to be transmitted Tx_Array Pointer to the array of values that are to be transmitted Because I C communication works byte wise a field of bytes is used for example unsigned char values Byte_CountRx Number of bytes to be received This parameter is defined only if an I C receive operation is necessary otherwise a zero is passed Rx_Array Pointer to the array used to store the received values Because IC communication works byte wise a field of bytes is used for example unsigned char values This parameter is defined only if an I C receive operation is necessary otherwise a zero is passed AckPointer Pointer to store the status of the 1 C operation ACK NACK PMBus Interface Functions There are two files that implement the PMBus interface one that uses PEC PMBus_PECfn c and one that does not PMBusfn c One or the other should be used in a given PMBus application depending on whether or not PEC functionality is to be used The files are identical except that the PMBus_PECfn c file includes an extra function to generate the PEC byte Similarly there are two header files PMBUS h and PMBUS_PEC h The latter should be used if PEC functionality is needed The PMBus_Init Slave_Address function is common to both files PMBus Init Slave_Address This function must be called only once at the start to initialize the MSP430 for PMBus functionality This includes initializing two GPIO pins for the alert
32. s SLAA386A January 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI 1 Submit Documentation Feedback 3 TEXAS INSTRUMENTS www ti com Introduction Introduction The Power Management Bus PMBus is an industry wide standard that can be viewed as a step toward unifying communication standards for power conversion and digital power management devices It was developed by the PMBus Implementers Forum PMBus IF The standard uses the widely accepted Inter Integrated Circuit C communication protocol for the hardware interface A number of additional features serve to enhance the basic I C communication protocol The PMBus standard is also considered to be an extension to the System Management Bus SMBus protocol that was popularized by the SBS Implementers Forum for battery systems 1 This application report serves as a guide to implementing the PMBus protocol on MSP430 host microcontroller devices with the USCI module An example application is used to demonstrate the master MSP430 PMBus interface with a UCD9112 buck controller PMBus Protocol The PMBus standard was developed by a group of companies that envisioned the need for a power management protocol that has a well defined physical communication layer and includes support for implementing commonly used power management commands 1 C was considered the preferred standard for implementing the physical communication layer because it provided a simple means to
33. trical connections between the MSP430 and the UCD9112 device The UCD9112 requires 9 V to 12 V input voltage and is capable of providing a varying output voltage of 1 V to 4 V See the device data sheet for more information 6 The PMBus clock data and alert response lines are tied to a 3 3 V 100 mA bus using 10 kQ resistors The MSP430 USCI module provides C support and the clock and data lines are interfaced to the slave device accordingly The 1 C output waveforms can be viewed and recorded using a bus analyzer tool such as the Total Phase Beagle Protocol Analyzer www totalphase com SLAA386A January 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI 7 Submit Documentation Feedback 3 TEXAS INSTRUMENTS www ti com Example Application Using the UCD9112 Synchronous Buck Controller Slave Sa 3 3 V at 100 mA 10kQS 10kQS 10 k2Q UCBOSDA 10Vto12V 32 768 kHz UCBOSCL P1 4 UCD9112 MSP430xG461x evil CONTROL 1Vto4V 8 LED Figure 7 MSP430 PMBus Interface to UCD9112 Port pins P1 4 and P4 2 are used for the SMBALERT and the CONTROL lines P1 4 interrupt P1IE is enabled to trigger on high low transitions The control line is configured as an output and is driven high by the MSP430 in the initialization routine This is because the slave device is configured to turn its output on or off based on both the control line and the reception of the OPERATION command Therefore the device
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35. y 2008 Revised February 2008 PMBus Implementation Using the MSP430 USCI 9 Submit Documentation Feedback 3 TEXAS INSTRUMENTS www ti com Function Description 5 1 4 5 2 5 2 1 10 TI_USCI_I2C_Transmit Byte_CountTx Tx_Array Byte_CountRx Rx_Array unsigned char AckPointer This function initializes all the variables necessary to perform a transmit operation In cases where the transmit operation needs to be followed by a restart and a receive operation additional parameters must be initialized The function first checks to see if the last two parameters Byte_CountRx and Rx_Array are defined If these parameters are non zero values the USCI module is configured to transmit the required number of bytes and send out an IC restart condition which is then followed by a receive operation If the last two parameters are zero then the USCI module is configured to perform a transmit only operation The AckPointer variable is used to return the status of the I C transaction A zero is returned if the transaction was successful ACK otherwise a one is returned NACK This function also initializes Timer A at the start of transmit operation The timer is set to expire at 35 ms timeout functionality of PMBus if no activity occurs on the I C bus during that period It uses ACLK as the clock source The following parameters are passed as arguments to this function Name Description Byte_CountTx Numbe
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