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Philips Semiconductors Preliminary User Manual ARM-based Microcontroller I 2 C State Service Routines Figure 34: Forced Access to a Busy I 2 C Bus Figure 35: Recovering from a Bus Obstruction Caused by a Low Level on SDA LPC2131/2132/2138 This section provides examples of operations that must be performed by various I 2 C state service routines. This includes: Initialization of the I2C block after a Reset. I2C Interrupt Service The 26 state service routines providing support for all four I2C operating modes. Initialization STA flag STO flag SDA line SCL line STA flag SDA line SCL line (1) time limit 1. Unsuccessful attempt to send a Start condition. 2. SDA line released. 3. Successful attempt to send a Start condition; state 08H is entered. In the initialization example, the I 2 C block is enabled for both master and slave modes. For each mode, a buffer is used for transmission and reception. The initialization routine performs the following functions: I2ADR is loaded with the part’s own slave address and the general call bit (GC) The I2 C interrupt enable and interrupt priority bits are set (1) Start condition (2) (3) Start condition I2C Interfaces I2C0 and I2C1 142 November 22, 2004
Philips Semiconductors Preliminary User Manual ARM-based Microcontroller LPC2131/2132/2138 The slave mode is enabled by simultaneously setting the I2EN and AA bits in I2CON and the serial clock frequency (for master modes) is defined by loading CR0 and CR1 in 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 general call. If the general call or the own slave address is detected, an interrupt is requested and I2STAT is loaded with the appropriate state information. I 2 C Interrupt Service When the I 2 C interrupt is entered, I2STAT contains a status code which identifies one of the 26 state services to be executed. The State Service Routines Each state routine is part of the I 2 C interrupt routine and handles one of the 26 states. Adapting State Services to an Application The state service examples show the typical actions that must be performed in response to the 26 I 2 C state codes. If one or more of the four I 2 C operating modes are not used, the associated state services can be omitted, as long as care is taken that the those states can never occur. In an application, it may be desirable to implement some kind of timeout during I 2 C operations, in order to trap an inoperative bus or a lost service routine. I2C Interfaces I2C0 and I2C1 143 November 22, 2004
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