ST92195D datasheet(188/249 Pages) STMICROELECTRONICS

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ST92195C/D - TWO-CHANNEL I2C BUS INTERFACE (I2C)

I2C BUS INTERFACE (Cont’d)

Master Receiver

Following the address transmission and acknowl-

edgment, the master receives bytes from the SDA

line into the I2CDR register via the internal shift

sequence:

– Acknowledge pulse according to the

SEND_ACK bit value,

– An interrupt is generated and the INT bit of the

I2CSTR2 register is set.

Then read the I2CDR register to store the trans-

mitted data.

Note: In order to generate the non-acknowledge

pulse after the last received data byte, the

SEND_ACK bit must be set just before reading the

second last data byte.

Master Transmitter

Following the address transmission and acknowl-

edgment, the master sends bytes from the I2CDR

ter.

When the acknowledge bit is received, the inter-

face generates an interrupt and sets the INT bit of

the I2CSTR2 register.

The user can check the ACK_BIT bit of the

I2CSTR1 register in order to handle the transac-

tion properly.

Closing a master communication

The master interface will generate a stop condition

on the bus when the user sets the STOP bit of the

I2CSTR1 register.

7.10.4 Interrupt Handling

To acknowledge interrupts generated by the I2C

interface, software must write any value in the

I2CDR register before leaving the I2C interrupt

subroutine. This is necessary in all modes includ-

ing slave or master receiver mode.

7.10.5 Error Cases

Each time an error occurs, an interrupt is generat-

ed. Then by checking the following bits, the user

can identify the problem:

– If the ERROR bit in the I2CSTR1 register is set,

an illegal start or stop condition has been detect-

ed.

If the AFEN bit in the I2CCTR register is set, the

UNPROC, UNEXP, and MISP bits of the

I2CSTR2 register indicate what kind of illegal

condition has been detected.

– If the ARB_LOST bit, in the I2CSTR1 register is

set, an arbitration lost occurred on the bus.

Note: the ERROR bit has higher priority than the

ARB_LOST bit, so if ERROR is set, ARB_LOST

has to be ignored.

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