ST72F521 datasheet(123/215 Pages) STMICROELECTRONICS

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ST72F521, ST72521B

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I2C BUS INTERFACE (Cont’d)

10.7.7 Register Description

I2C CONTROL REGISTER (CR)

Read / Write

Reset Value: 0000 0000 (00h)

Bit 7:6 = Reserved. Forced to 0 by hardware.

Bit 5 = PE Peripheral enable.

This bit is set and cleared by software.

0: Peripheral disabled

1: Master/Slave capability

Notes:

– When PE=0, all the bits of the CR register and

the SR register except the Stop bit are reset. All

outputs are released while PE=0

– When PE=1, the corresponding I/O pins are se-

lected by hardware as alternate functions.

– To enable the I2C interface, write the CR register

TWICE with PE=1 as the first write only activates

the interface (only PE is set).

Bit 4 = ENGC Enable General Call.

This bit is set and cleared by software. It is also

cleared by hardware when the interface is disa-

bled (PE=0). The 00h General Call address is ac-

knowledged (01h ignored).

0: General Call disabled

1: General Call enabled

Note: In accordance with the I2C standard, when

GCAL addressing is enabled, an I2C slave can

only receive data. It will not transmit data to the

master.

Bit 3 = START Generation of a Start condition.

This bit is set and cleared by software. It is also

cleared by hardware when the interface is disa-

bled (PE=0) or when the Start condition is sent

(with interrupt generation if ITE=1).

– In master mode:

0: No start generation

1: Repeated start generation

– In slave mode:

0: No start generation

1: Start generation when the bus is free

Bit 2 = ACK Acknowledge enable.

This bit is set and cleared by software. It is also

cleared by hardware when the interface is disa-

bled (PE=0).

0: No acknowledge returned

1: Acknowledge returned after an address byte or

a data byte is received

Bit 1 = STOP Generation of a Stop condition.

This bit is set and cleared by software. It is also

cleared by hardware in master mode. Note: This

bit is not cleared when the interface is disabled

(PE=0).

– In master mode:

0: No stop generation

1: Stop generation after the current byte transfer

or after the current Start condition is sent. The

STOP bit is cleared by hardware when the Stop

condition is sent.

– In slave mode:

0: No stop generation

1: Release the SCL and SDA lines after the cur-

rent byte transfer (BTF=1). In this mode the

STOP bit has to be cleared by software.

Bit 0 = ITE Interrupt enable.

This bit is set and cleared by software and cleared

by hardware when the interface is disabled

(PE=0).

0: Interrupts disabled

1: Interrupts enabled

Refer to Figure 67 for the relationship between the

events and the interrupt.

SCL is held low when the ADD10, SB, BTF or

ADSL flags or an EV6 event (See Figure 66) is de-

tected.

ENGC START

ACK

STOP

ITE

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