UPSD3422_V01 datasheet(138/300 Pages) STMICROELECTRONICS

138 / 300 page

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I2C interface

UPSD3422, UPSD3433, UPSD3434, UPSD3454

138/300

23.13.1

Interrupt service routine (ISR)

A typical I2C interrupt service routine would handle a interrupt for any of the four

combinations of Master/Slave and Transmitter/Receiver. In the example routines above, the

firmware sets global variables, I2C_master and I2C_xmitter, before enabling interrupts.

These flags tell the ISR which one of the four cases to process. Following is pseudo-code for

high-level steps in the I2C ISR:

Begin I2C ISR <I2C interrupt just occurred>:

Clear I2C interrupt flag:

–

S1STA.INTR = 0

Read status of SIOE, put in to variable, status

–

status = S1STA

Read global variables that determine the mode

–

mode <= (I2C_master, I2C_slave)

If mode is Master-Transmitter

Bus Arbitration lost? (status.BLOST=1?)

If Yes, Arbitration was lost:

–

S1DAT = dummy, write to release bus

–

Exit ISR, SIOE will switch to Slave Recv mode

If No, Arbitration was not lost, continue:

ACK recvd from Slave? (status.ACK_RESP=0?)

If No, an ACK was not received:

–

S1CON.STO = 1, set Stop bus condition

–

–

S1DAT = dummy, write to release bus

–

Exit ISR

If Yes, ACK was received, then continue:

–

S1DAT = xmit_buf[buffer_index], transmit byte

Was that the last byte of data to transmit?

If No, it was not the last byte, then:

–

Exit ISR, transmit next byte on next interrupt

If Yes, it was the last byte, then:

–

S1CON.STO = 1, set Stop bus condition

–

S1DAT = dummy, write to release bus

–

Exit ISR

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UPSD3422 Datasheet(PDF) 138 Page - STMicroelectronics

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