ST72C254G2 datasheet(77/135 Pages) STMICROELECTRONICS

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I2C BUS INTERFACE (Cont’d)

Master Transmitter

Following the address transmission and after SR1

from the DR register to the SDA line via the inter-

nal shift register.

The master waits for a read of the SR1 register fol-

lowed by a write in the DR register, holding the

SCL line low (see Figure 45 Transfer sequencing

EV8).

When the acknowledge bit is received, the

interface sets:

– EVF and BTF bits with an interrupt if the ITE bit

is set.

To close the communication: after writing the last

byte to the DR register, set the STOP bit to gener-

ate the Stop condition. The interface goes auto-

matically back to slave mode (M/SL bit cleared).

Error Cases

– BERR: Detection of a Stop or a Start condition

during a byte transfer. In this case, the EVF and

BERR bits are set by hardware with an interrupt

if ITE is set.

– AF: Detection of a non-acknowledge bit. In this

case, the EVF and AF bits are set by hardware

with an interrupt if the ITE bit is set. To resume,

set the START or STOP bit.

– ARLO: Detection of an arbitration lost condition.

In this case the ARLO bit is set by hardware (with

an interrupt if the ITE bit is set and the interface

goes automatically back to slave mode (the M/SL

bit is cleared).

Note: In all these cases, the SCL line is not held

low; however, the SDA line can remain low due to

possible «0» bits transmitted last. It is then neces-

sary to release both lines by software.

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