Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
923
I
2
C Bus Interface Units—Intel
®
81341 and 81342
Wait for
Acknowledge
from slave-
receiver
Master-transmit
only
• As a master-transmitter, the I
2
C Bus Interface Unit generates the clock for the
acknowledge pulse. The I
2
C Bus Interface Unit is responsible for releasing the
SDA
line
to allow slave-receiver Ack transmission.
.
Read one byte of
I
2
C Data from
the IDBR
Master-receive
only
• Data receive mode of I
2
C master operation.
• Eight bits are read from the serial bus, collected in the shift register then transferred to
the IDBR after the Ack/Nack bit is read.
• The Intel XScale
®
processor reads the IDBR when the IDBR Receive Full bit is set and
the Transfer Byte bit is clear. When enabled, a IDBR Receive Full Interrupt is signalled to
the Intel XScale
®
microarchitecture.
• When the IDBR is read, when the Ack/Nack Status is clear (indicating Ack), the Intel
XScale
®
processor writes the Ack/Nack Control bit and set the Transfer Byte bit to
initiate the next byte read.
• When the Ack/Nack Status bit is set (indicating Nack), Transfer Byte bit is clear, STOP
bit in the ICR is set, and Unit Busy bit in the ISR is set, then the last data byte has been
read into the IDBR and the I
2
C Bus Interface Unit is sending the STOP.
• When the Ack/Nack Status bit is set (indicating Nack), Transfer Byte bit is clear, but the
STOP bit is clear, then the Intel XScale
®
processor has two options: 1. set the START
bit, write a new target address to the IDBR, and set the Transfer Byte bit which sends a
repeated start condition, 2. set the Master Abort bit and leave the Transfer Byte clear
which sends a STOP only.
Transmit
Acknowledge to
slave-
transmitter
Master-receive
only
• As a master-receiver, the I
2
C Bus Interface Unit generates the clock for the
acknowledge pulse. The I
2
C Bus Interface Unit is also responsible for driving the
SDA
line during the Ack cycle.
• When the next data byte is to be the last transaction, the Intel XScale
®
processor sets
the Ack/Nack Control bit for Nack generation.
.
Generate a
Repeated START
to chain I
2
C
transactions
Master-transmit
Master-receive
• When data chaining is desired, a repeated START condition is used instead of a STOP
condition.
• This occurs after the last data byte of a transaction has been written to the bus.
• The Intel XScale
®
processor writes the next target slave address and the R/W# bit to
the IDBR, set the START bit, and set the Transfer Byte bit.
.
Generate a STOP Master-transmit
Master-receive
• Generated after the Intel XScale
®
processor writes the last data byte on the bus.
• Intel XScale
®
processor generates a STOP condition by setting the STOP bit in the ICR.
.
Table 584. Master Transactions (Sheet 2 of 2)
I
2
C Master
Action
Mode of
Operation
Definition