ST92F124 datasheet(264/429 Pages) STMICROELECTRONICS

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I2C BUS INTERFACE

I2C BUS INTERFACE (Cont’d)

The following seven registers are used to handle

the interrupt and the DMA features:

– Interrupt Status Register I2CISR

– Interrupt Mask Register I2CIMR

– Interrupt Vector Register I2CIVR

– Receiver DMA Address Pointer Register

I2CRDAP

– Receiver DMA Transaction Counter Register

I2CRDC

– Transmitter DMA Address Pointer Register

I2CTDAP

– Transmitter DMA transaction Counter Register

I2CTDC

The interface can decode both addresses:

– Software programmable 7-bit General Call

address

– I2C address stored by software in the I2COAR1

I2COAR1 and I2COAR2 registers in 10-bit ad-

dress mode.

After a reset, the interface is disabled.

IMPORTANT:

1. To guarantee correct operation, before enabling

the peripheral (while I2CCR.PE=0), configure bit7

and bit6 of the I2COAR2 register according to the

internal clock INTCLK (for example 11xxxxxxb in

the range 14 - 30 MHz).

2. Bit7 of the I2CCR register must be cleared.

10.8.3.1 Mode Selection

In I2C mode, the interface can operate in the four

following modes:

– Master transmitter/receiver

– Slave transmitter/receiver

By default, it operates in slave mode.

This interface automatically switches from slave to

master after a start condition is generated on the

bus and from master to slave in case of arbitration

loss or stop condition generation.

In Master mode, it initiates a data transfer and

generates the clock signal. A serial data transfer

always begins with a start condition and ends with

a stop condition. Both start and stop conditions are

generated in master mode by software.

In Slave mode, it is able to recognize its own ad-

dress (7 or 10-bit), as stored in the I2COAR1 and

I2COAR2 registers and (when the I2CCR.ENGC

bit is set) the General Call address (stored in

I2CADR register). It never recognizes the Start

Byte (address byte 01h) whatever its own address

is.

Data and addresses are transferred in 8 bits, MSB

first. The first byte(s) following the start condition

contain the address (one byte in 7-bit mode, two

bytes in 10-bit mode). The address is always

transmitted in master mode.

A 9th clock pulse follows the 8 clock cycles of a

byte transfer, during which the receiver must send

acknowledge

bit

the

transmitter.

Acknowledge is enabled and disabled by software.

Refer to Figure 127.

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