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Registers
Table 7. I2C Interrupt Status Register (ICSTR) Field Descriptions (continued)
Bit Field Value Description
1 NACK No-acknowledgment interrupt flag bit. NACK applies when the I2C is a transmitter (master or slave).
NACK indicates whether the I2C has detected an acknowledge bit (ACK) or a no-acknowledge bit
(NACK) from the receiver. The CPU can poll NACK or use the NACK interrupt request.
0 ACK received/NACK is not received. NACK is cleared by one of the following events:
• An acknowledge bit (ACK) has been sent by the receiver.
• NACK is manually cleared. To clear this bit, write a 1 to it.
• The CPU reads the interrupt vector register (ICIVR) when the register contains the code for a NACK
interrupt.
• The I2C is reset (either when 0 is written to the IRS bit of ICMDR or when the processor is reset).
1 NACK bit is received. The hardware detects that a no-acknowledge (NACK) bit has been received.
Note: While the I2C performs a general call transfer, NACK is 1, even if one or more slaves send
acknowledgment.
0 AL Arbitration-lost interrupt flag bit (only applicable when the I2C is a master-transmitter). AL primarily
indicates when the I2C has lost an arbitration contest with another master-transmitter. The CPU can poll
AL or use the AL interrupt request.
0 Arbitration is not lost. AL is cleared by one of the following events:
• AL is manually cleared. To clear this bit, write a 1 to it.
• The CPU reads the interrupt vector register (ICIVR) when the register contains the code for an AL
interrupt.
• The I2C is reset (either when 0 is written to the IRS bit of ICMDR or when the processor is reset).
1 Arbitration is lost. AL is set by one of the following events:
• The I2C senses that it has lost an arbitration with two or more competing transmitters that started a
transmission almost simultaneously.
• The I2C attempts to start a transfer while the BB (bus busy) bit is set to 1.
When AL is set to 1, the MST and STP bits of ICMDR are cleared, and the I2C becomes a
slave-receiver.
27
SPRUEN0D–March 2011 Inter-Integrated Circuit (I2C) Peripheral
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