![Intel IXP45X Скачать руководство пользователя страница 878](http://html1.mh-extra.com/html/intel/ixp45x/ixp45x_developers-manual_2073092878.webp)
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—I2C Bus Interface Unit
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
878
Order Number: 306262-004US
also be used instead of interrupts, although it would be very cumbersome.
shows a block diagram of the I
2
C Bus Interface Unit and its interface to
the internal bus.
The I
2
C Bus Interface Unit consists of the two wire interface to the I
2
C bus, an 8-bit
buffer for passing data to and from the processor, a set of control and status registers,
and a shift register for parallel/serial conversions.
The I
2
C Bus Interface Unit can initiate an interrupt when a buffer is full, buffer empty,
slave address detected, arbitration lost, or bus error condition occurs. All interrupt
conditions must be cleared explicitly by software. See
“I2C Status Register - ISR” on
for details.
The I
2
C Data Buffer Register (IDBR) is an 8-bit data buffer that receives a byte of data
from the shift register interface of the I
2
C bus on one side and parallel data from the
processor’s internal bus on the other side. The serial shift register is not user
accessible.
The control and status registers are located in the I
2
C memory-mapped address space.
The registers and their function are defined in
“Register Definitions” on page 896
.
The I
2
C Bus Interface Unit supports fast mode operation of 400 Kbps. Fast-mode logic
levels, formats, and capacitive loading, and protocols are exactly the same as the
100 Kbps, standard mode. Because the data setup and hold times differ between the
fast and standard mode, the I
2
C has been designed to meet the faster, standard mode
requirements for these two specifications. Refer to the I
2
C Bus Specification for details.
21.4.2
I
2
C Bus Interface Modes
The I
2
C Bus Interface Unit can be in different modes of operation to accomplish a
transfer.
summarizes the different modes.
While the I
2
C Bus Interface Unit is in idle mode (neither receiving or transmitting serial
data), the unit defaults to Slave-Receive mode. This allows the interface to monitor the
bus and receive any slave addresses that might be intended for the IXP45X/IXP46X
network processors.
Table 277.
Modes of Operation
Mode
Definition
Master - Transmit
I
2
C Bus Interface Unit acts as a master.
Used for a write operation.
I
2
C Bus Interface Unit sends the data.
I
2
C Bus Interface Unit is responsible for clocking.
Slave device will be in slave-receive mode
Master - Receive
I
2
C Bus Interface Unit acts as a master.
Used for a read operation.
I
2
C Bus Interface Unit receives the data.
I
2
C Bus Interface Unit is responsible for clocking.
Slave device will be in slave-transmit mode
Slave - Transmit
I
2
C Bus Interface Unit acts as a slave.
Used for a read (master) operation.
I
2
C Bus Interface Unit sends the data.
Master device will be in master-receive mode.
Slave - Receive (default)
I
2
C Bus Interface Unit acts as a slave.
Used for a write (master) operation.
I
2
C Bus Interface Unit receives the data.
Master device will be in master-transmit mode.