UM10139

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Philips SemiconductorsVolume 1<strong>UM10139</strong>Chapter 11: I 2 C interfacesSSLAWADATAASOTHER MASTER CONTINUESPSSLA08H18H28H08HOther Master sends RepeatedStart earlierRetryFig 37. Simultaneous repeated START conditions from two mastersSTA FlagTime limitSTO FlagSDA LineSCL LineStart conditionFig 38. Forced access to a busy I 2 C-busSTA Flag(2)(3)SDA Line(1)(1)SCL LineStart condition1. Unsuccessful attempt to send a Start condition.2. SDA Line released.3. Succcessful attempt to send a Start condition; state 08H is entered.Fig 39. Recovering from a bus obstruction caused by a low level on SDA11.8.14 I 2 C State service routinesThis section provides examples of operations that must be performed by various I 2 C stateservice routines. This includes:• Initialization of the I 2 C block after a Reset.• I 2 C Interrupt Service© Koninklijke Philips Electronics N.V. 2005. All rights reserved.User manual Rev. 01 — 15 August 2005 162
Philips SemiconductorsVolume 1<strong>UM10139</strong>Chapter 11: I 2 C interfaces• The 26 state service routines providing support for all four I 2 C operating modes.11.8.15 InitializationIn the initialization example, the I 2 C block is enabled for both master and slave modes. Foreach mode, a buffer is used for transmission and reception. The initialization routineperforms the following functions:• I2ADR is loaded with the part’s own slave address and the general call bit (GC)• The I 2 C interrupt enable and interrupt priority bits are set• The slave mode is enabled by simultaneously setting the I2EN and AA bits in I2CONand the serial clock frequency (for master modes) is defined by loading CR0 and CR1in I2CON. The master routines must be started in the main program.The I 2 C hardware now begins checking the I 2 C-bus for its own slave address and generalcall. If the general call or the own slave address is detected, an interrupt is requested andI2STAT is loaded with the appropriate state information.11.8.16 I 2 C interrupt serviceWhen the I 2 C interrupt is entered, I2STAT contains a status code which identifies one ofthe 26 state services to be executed.11.8.17 The State service routinesEach state routine is part of the I 2 C interrupt routine and handles one of the 26 states.11.8.18 Adapting State services to an application11.9 Software exampleThe state service examples show the typical actions that must be performed in responseto the 26 I 2 C state codes. If one or more of the four I 2 C operating modes are not used, theassociated state services can be omitted, as long as care is taken that the those statescan never occur.In an application, it may be desirable to implement some kind of timeout during I 2 Coperations, in order to trap an inoperative bus or a lost service routine.11.9.1 Initialization routineExample to initialize I 2 C Interface as a Slave and/or Master.1. Load I2ADR with own Slave Address, enable general call recognition if needed.2. Enable I 2 C interrupt.3. Write 0x44 to I2CONSET to set the I2EN and AA bits, enabling Slave functions. ForMaster only functions, write 0x40 to I2CONSET.11.9.2 Start Master Transmit functionBegin a Master Transmit operation by setting up the buffer, pointer, and data count, theninitiating a Start.© Koninklijke Philips Electronics N.V. 2005. All rights reserved.User manual Rev. 01 — 15 August 2005 163
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UM10139

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