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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
899
I2C Bus Interface Unit—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
21.10.2
I
2
C Status Register - ISR
I
2
C
interrupts are signalled to the interrupt controller of the IXP45X/IXP46X network
processors by the I
2
C
Interrupt Status Register (ISR). Software uses the ISR bits to
check the status of the I
2
C unit and bus. ISR bits (bits 9-5) are updated after the Ack/
Nack bit has completed on the I
2
C bus.
The ISR is also used to clear interrupts signalled from the I
2
C Bus Interface Unit. These
are:
• IDBR Receive Full
• IDBR Transmit Empty
• Slave Address Detected
• Bus Error Detected
• STOP Condition Detect
• Arbitration Lost
03
Transfer Byte
Transfer Byte: used to send/receive a byte on the I
2
C bus.
0 = Cleared by I
2
C unit when the byte is sent/received.
1 = Send/receive a byte.
The IXP45X/IXP46X network processors
c
an monitor this bit to
determine when the byte transfer has completed. In master or slave
mode, after each byte transfer including Ack/Nack bit, the I
2
C unit
holds the SCL line low (inserting wait states) until the Transfer Byte bit
is set.
0
RW
02
Ack/Nack
Control
Ack/Nack Control: defines the type of Ack pulse sent by the I
2
C unit
when in master receive mode.
0 = The I
2
C unit sends an Ack pulse after receiving a data byte.
1 = The I
2
C unit sends a negative Ack (Nack) after receiving a data
byte.
The I
2
C unit automatically sends an Ack pulse when responding to its
slave address or when responding in slave-receive mode, independent
of the Ack/Nack control bit setting.
0
RW
01
STOP
STOP: used to initiate a STOP condition after transferring the next
data byte on the I
2
C bus when in master mode. In master-receive
mode, the Ack/Nack control bit must be set in conjunction with this
bit. See
Section 21.4.3.3, “STOP Condition” on page 881
for more
details on the STOP state.
0 = Do not send a STOP.
1 = Send a STOP.
0
RW
00
START
START: used to initiate a START condition to the I
2
C unit when in
Section 21.4.3.1, “START Condition” on page 880
for more details on the START state.
0 = Do not send a START.
1 = Send a START.
0
RW
Register
I
2
C Control Register (Sheet 3 of 3)
Bits
Name
Description
Reset
Value
Access
Register Name:
I
2
C Status Register - ISR
Block
Base Address:
0xC801_1004
Offset Address
Reg
OffsetAddress
Reset Value
0x0000_0000
Register Description:
I
2
C Status Register - ISR
Access:
(See below.)
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)
See table below.