Intel® PXA255 Processor Developer’s Manual 9-27

I2C Bus Interface Unit
9.9.5 I2C Slave Address Register (ISAR)

The ISAR, shown in Table 9- 12, defines the I2C unit’s 7-bit slave address. In slave-receive mode,

the processor responds when the 7-bit address matches the value in this register. The processor

writes this register before it enables I2C operations . T he ISAR is f ull y p rogr ammab le ( no add ress is

assigned to the I2C unit) so it can be set to a value other than those of hard-wired I2C slave

peripherals in the system. If the processor is reset, the ISAR is not affected. The ISAR register

default value is 00000002.

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

1 ACKNAK
ACK/NAK Status:
0 = I2C unit received or sent an ACK on the bus.
1 = I2C unit received or sent a NAK.
Used in slave-transmit mode to determine when the transferred byte is the last one.
Updated after each byte and ACK/NAK information is received.
0RWM
Read/Write Mode:
0 = I2C unit is in master-transmit or slave-receive mode.
1 = I2C unit is in master-receive or slave-transmit mode.
R/nW bit of the slave address. Automatically cleared by hardware after a stop state.

Table 9-11. ISR Bit Definitions (Sheet 2 of 2)

Physical Address
4030_1698 I2C Status 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
BED
SAD
GCAD
IRF
ITE
ALD
SSD
IBB
UB
ACKNAK
RWM
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 0

Table 9-12. ISAR Bit Definitions

Physical Address
4030_16A0 I2C Slave Address 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 ISA
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 0
31:7 — reserved
6:0 ISA I2C Slave Address: 7-bit address that the I2C unit responds to when in slave-receive
mode.