AN1713/0803 1/4 AN1713 application note smbus slave driver for st7 i2c peripheral by microcontroller division applications introduction the goal of this application note is to implement the smbus slave protocol using st7 i2c. the software of this application performs all smbus bus protocols mentioned in smbus v1.1. the device chosen here is st72f264 which has multi-master i2c capability. the program described in this application note is in c language. the driver is compatible with metrowerks and cosmic compilers. 1 characteristics the main characteristics of this smbus slave driver are: n smbus bus protocols: quick command, send/ receive byte, write/ read byte, write/ read word, write/ read block, process call word/ block n slave smbus addressing n crc-8 packet error checking for more details please refer to the smbus specification v1.1. 2 smbus 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. 2.1 similarities of smbus and i2c n 2 wire bus protocol (1 clk, 1 data) n master-slave communication, master provides clock n multi master capability n smbus data format similar to i2c 7-bit addressing format. 1
2/4 smbus slave driver for st7 i2c peripheral figure 1. data transfer format smbdat: smbus data line smbclk: smbus clock line 2.2 differences between smbus and i2c the following table describes the differences between smbus and i2c. table 1. smbus vs i2c 2.3 smbus application with system management bus, a device can provide manufacturer information, tell the system what its model/part number is, save its state for a suspend event, report different types of errors, accept control parameters, and return its status. smbus provides a control bus for system and power management related tasks. smbus st7 i2c max. speed 100 khz max. speed 400 khz min. clock speed 10 khz no minimum clock speed 35ms clock low time-out no time-out logic levels are fixed logic levels are vdd dependent different address types (reserved, dynamic etc.) 7-bit, 10-bit and general call slave address types different bus protocols (quick command, proc- ess call etc.) no bus protocols packet error checking (pec) implemented no packet error checking. only error status indication 2
3/4 smbus slave driver for st7 i2c peripheral section 3 contains the description of the smbus driver. these functions available with the driver configure the st7 i2c peripheral as an smbus slave and allow it to communicate with any smbus master. here all smbus v1.1 features are supported. this driver can be used in the smart battery system and other low-power devices. for more details about the functions please refer to the smbs_um.pdf file. 3 software the software and user manual are available in the zip file supplied with this application note. the user manual explains how to use the smbus slave functions. an example is also pro- vided to help the user to write an application using smbus functions. the following lists the source files which can be used for the smbus slave interface. they are separated into 2 types. 1. user accessible files: following files can be modified by the user depending on the requirement. main.c: contains the example program for smbus slave driver communication for write word, write block and read word protocols. here the pec option is not chosen. smbs_config.h: select the cpu frequency and packet error checking option 2. non-user accessible files: these files should not be modified by the user. smbs.c: contains source code for all the slave smbus functions smbs.h: contains prototypes for all the slave smbus functions smbs_hr.c: contains all the i2c hardware registers smbs_hr.h: declares all the hardware registers as extern this software is tested only for write word, read word and write block protocols.
4/4 smbus slave driver for st7 i2c peripheral the present note which is for guidance only aims at providing customers with information regarding their products in order for them to save time. as a result, stmicroelectronics shall not be held liable for any direct, indirect or consequential damages with respect to any claims arising from the content of such a note and/or the use made by customers of the information contained herein in connection with their products. information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the co nsequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specifications mentioned in this publicati on are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectronics prod ucts are not authorized for use as critical components in life support devices or systems without the express written approval of stmicroele ctronics. the st logo is a registered trademark of stmicroelectronics ? 2003 stmicroelectronics - all rights reserved. purchase of i 2 c components by stmicroelectronics conveys a license under the philips i 2 c patent. rights to use these components in an i 2 c system is granted provided that the system conforms to the i 2 c standard specification as defined by philips. stmicroelectronics group of companies australia - brazil - canada - china - finland - france - germany - hong kong - india - israel - italy - japan malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - u.s.a. http://www.st.com
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