UPSD3354DV-40U6 Datasheet, PDF (137/272 Pages) STMicroelectronics – fast 8032 MCU with programmable logic

UPSD33xx
I²C interface
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?)}
t(s If Yes, Arbitration was lost:
c _{● S1DAT = dummy, write to release bus}
du _{● Exit ISR, SIOE will switch to Slave Recv mode}
ro _{If No, Arbitration was not lost, continue:}
P _{ACK recvd from Slave? (status.ACK_RESP=0?)}
te _{If No, an ACK was not received:}
le _{● S1CON.STO = 1, set STOP bus condition}
so _{● <STOP occurs after ISR exit>}
b _{● S1DAT = dummy, write to release bus}
- ^O ● Exit ISR
) _{If Yes, ACK was received, then continue:}
t(s ● S1DAT = xmit_buf[buffer_index], transmit byte
uc Was that the last byte of data to transmit?
d _{If No, it was not the last byte, then:}
ro _{● Exit ISR, transmit next byte on next interrupt}
P _{If Yes, it was the last byte, then:}
te_{● S1CON.STO = 1, set STOP bus condition}
le _{<STOP occurs after ISR exit>}
so _{● S1DAT = dummy, write to release bus}
Ob ^{● Exit ISR}
Doc ID 9685 Rev 7
137/272