AN355 Si5040 TW O -B YTE R EAD I 2 C P ROTOCOL 1. Introduction Silicon Labs has found that some MCUs do not support the normal I2C master read protocol of a repeated start. Fortunately, the Si5040 can support an alternate 2-command read sequence. This protocol should only be used in a single-master bus since the master has to release the bus between commands. S Slave Address 0 A Byte Address A S Slave Address 1 A Data A Data N P Figure 1. Normal I2C Repeated Start Read Sequence S Slave Address 0 A Byte Address A S Slave Address 1 A Data A P Data N P Figure 2. Alternate 2 Command I2C Read Sequence From master to slave From slave to master 1 – Read 0 – Write A – Acknowledge (SDA LOW) N – Not Acknowledge (SDA HIGH). Required after the last data byte to signal the end of the read comand to the slave. S – START condition P – STOP condition Rev. 0.1 10/08 Copyright © 2008 by Silicon Laboratories AN355 ClockBuilder Pro One-click access to Timing tools, documentation, software, source code libraries & more. Available for Windows and iOS (CBGo only). www.silabs.com/CBPro Timing Portfolio www.silabs.com/timing SW/HW Quality Support and Community www.silabs.com/CBPro www.silabs.com/quality community.silabs.com Disclaimer Silicon Laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers using or intending to use the Silicon Laboratories products. Characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and "Typical" parameters provided can and do vary in different applications. Application examples described herein are for illustrative purposes only. Silicon Laboratories reserves the right to make changes without further notice and limitation to product information, specifications, and descriptions herein, and does not give warranties as to the accuracy or completeness of the included information. Silicon Laboratories shall have no liability for the consequences of use of the information supplied herein. This document does not imply or express copyright licenses granted hereunder to design or fabricate any integrated circuits. The products must not be used within any Life Support System without the specific written consent of Silicon Laboratories. A "Life Support System" is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expected to result in significant personal injury or death. Silicon Laboratories products are generally not intended for military applications. Silicon Laboratories products shall under no circumstances be used in weapons of mass destruction including (but not limited to) nuclear, biological or chemical weapons, or missiles capable of delivering such weapons. Trademark Information Silicon Laboratories Inc., Silicon Laboratories, Silicon Labs, SiLabs and the Silicon Labs logo, CMEMS®, EFM, EFM32, EFR, Energy Micro, Energy Micro logo and combinations thereof, "the world’s most energy friendly microcontrollers", Ember®, EZLink®, EZMac®, EZRadio®, EZRadioPRO®, DSPLL®, ISOmodem ®, Precision32®, ProSLIC®, SiPHY®, USBXpress® and others are trademarks or registered trademarks of Silicon Laboratories Inc. ARM, CORTEX, Cortex-M3 and THUMB are trademarks or registered trademarks of ARM Holdings. Keil is a registered trademark of ARM Limited. All other products or brand names mentioned herein are trademarks of their respective holders. Silicon Laboratories Inc. 400 West Cesar Chavez Austin, TX 78701 USA http://www.silabs.com