Intel
®
81341 and 81342—I
2
C Bus Interface Units
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
938
Order Number: 315037-002US
16.8.4
I
2
C Data Buffer Register
x —
IDBR
x
The I
2
C Data Buffer Register (IDBRx) is used by the 8134881341 and 81342 to
transmit and receive data from the I
2
C bus. The accesses the IDBRx by the
8134881341 and 81342 on one side and by the I
2
C shift register on the other. Data
coming into the I
2
C Bus Interface Unit is received into the IDBRx after a full byte has
been received and acknowledged. Data going out of the I
2
C Bus Interface Unit is
written to the IDBRx by the Intel XScale
®
processor and sent to the serial bus.
When the I
2
C Bus Interface Unit is in transmit mode (master or slave), the
8134881341 and 81342 writes data to the IDBRx over the internal bus. This occurs
when a master transaction is initiated or when the IDBRx Transmit Empty Interrupt is
signalled. Data is moved from the IDBRx to the shift register when the Transfer Byte bit
is set. The IDBR Transmit Empty Interrupt is signalled (when enabled) when a byte has
been transferred on the I
2
C bus and the acknowledge cycle is complete. When the
IDBRx is not written by the 8134881341 and 81342 (and a STOP condition was not in
place) before the I
2
C bus is ready to transfer the next byte packet, the I
2
C Bus
Interface Unit inserts wait states until the Intel XScale
®
processor
writes the IDBRx
and sets the Transfer Byte bit.
When the I
2
C Bus Interface Unit is in receive mode (master or slave), the processor
reads IDBRx data over the internal bus. This occurs when the IDBRx Receive Full
Interrupt is signalled. The data is moved from the shift register to the IDBRx when the
Ack cycle is complete. The I
2
C Bus Interface Unit inserts wait states until the IDBR has
been read. Refer to
Section 16.3.2, “I2C Acknowledge” on page 919
for acknowledge
pulse information in receiver mode. After the 8134881341 and 81342 reads the IDBRx,
the Ack/Nack Control bit is written and the Transfer Byte bit is written, allowing the
next byte transfer to proceed on the I
2
C Bus. The IDBRx register is 00H after reset.
Table 591. I
2
C Data Buffer Register x — IDBRx
Bit
Default
Description
31:08
000000H Reserved
07:00
00H
I
2
C
Data Buffer
: Buffer for I
2
C bus send/receive data.
PCI
IOP
Attributes
Attributes
28
24
20
16
12
8
4
0
31
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
Unit #
0
1
2
Intel XScale
®
processor internal bus address
offset
+250CH
+252CH
+254CH
Attribute Legend:
RV = Reserved
PR = Preserved
RS = Read/Set
RW = Read/Write
RC = Read Clear
RO = Read Only
NA = Not Accessible