Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
869
SMBus Interface Unit—Intel
®
81341 and 81342
14.3.3.1 Data Transfer Examples
For
through
, the following terminology is used:
S
Start Bit
Sr
Start Repeat Bit
W
Write Command
R
Read Command
A
Acknowledge
N
Retry / not Acknowledge
P
Stop Bit
Clear boxes indicate phases of the cycle driven by the initiator, and shaded boxes
indicate phases of the cycle driven by the target.
14.3.3.2 Configuration and Memory Reads
81341 and 81342 supports only read dword to internal register space. All Configuration
and memory reads are accomplished through an SMBus write(s) and later followed by
an SMBus read to read the status and the read data. For SMBus read transactions, the
last byte of data (or the PEC byte when enabled), is NACKed by the master to indicate
the end of the transaction. The SMBus memory read command returns the status of the
previous internal command and the data associated previous internal read command.
The status field encoding is:
Examples of configuration and memory reads are shown in
through
. For the definition of the diagram conventions below, refer to the System
Management Bus Specification, Revision 2.0.
Table 549. SMBus Status Byte Encoding
Bit
Description
7
Reserved
6
Internal Address Error
5
Internal Master Abort
4
Internal Target Abort
3:1 Reserved
0
Successful
Figure 127. DWORD Configuration Read Protocol (SMBus Block Write/Block Read, PEC
Enabled)