Texas Instruments TMS320C642X manual An acknowledge bit ACK has been sent by the receiver

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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.

SPRUEN0D –March 2011	Inter-Integrated Circuit (I2C) Peripheral	27
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