Intel® PXA255 Processor Developer’s Manual 9-25
I2C Bus Interface Unit
9.9.4 I2C Status Register (ISR)

The ISR, shown in Table 9- 11, signals I2C interrupts to the processor interrupt controller. Software

can use the ISR bits to check the status of the I2C unit and bus. ISR bits (bits 9-5) are upda ted after

the ACK/NAK bit is completed on the I2C bus.

The ISR also clears the following interrupts signalled from the I2C unit:

IDBR Receive Full
IDBR Transmit Empty
Slave Address Detected
Bus Error Detected
STOP Condition Detect
Arbitration Lost

This is a read/wri te register. Ignore reads from reserved bit s. Write zeros to res erved bits.

2 ACKNAK
ACK/NAK Control: defines the type of ACK pulse sent by the I2C unit when in master-
receive mode.
0 = The I2C unit sends an ACK pulse after it receives a data byte.
1 = The I2C unit sends a negative ACK (NAK) after it receives a data byte.
The I2C unit automatically sends an ACK pulse when it responds to its slave address or
when it responds in slave-receive mode, independent of the ACK/NAK control bit setting.
1STOP
STOP: initiates a STOP condition after the next data byte on the I2C bus is transferred in
master mode. In master-receive mode, the ACK/NAK control bit must be set along with this
bit. See Section9.3.3.3 for more details on the STOP state.
0 = Do not send a STOP.
1 = Send a STOP.
0START
START: initiates a START condition to the I2C unit when in master mode. See
Section9.3.3.1 for more details on the START state.
0 = Do not send a START.
1 = Send a START.

Table 9-10. ICR Bit Definitions (Sheet 3 of 3)

Physical Address
4030_1690 I2C Control Register I2C Bus Interface Unit
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved
FM
UR
SADIE
ALDIE
SSDIE
BEIE
IRFIE
ITEIE
GCD
IUE
SCLE
MA
TB
ACKNAK
STOP
START
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0