Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
867
SMBus Interface Unit—Intel
®
81341 and 81342
14.3.3
Architecture
The 81341 and 81342 SMBus register interface consists of a set of registers that are
only accessible from the SMBus interface only and are shown in
and
. These registers are used to issue commands for reading and writing
configuration registers and memory locations on 81341 and 81342
shows
that register format for accessing configuration space.
shows the register
format for accessing memory space, The command register provides a bit that
indicates whether configuration or memory space ought to be accessed.
All SMBus accesses to internal register space are initiated via a write to the command
register (CMD). The command register indicates the access type (read or write) and
whether the command is targeting the configuration spaces or memory-mapped
registers. Any register writes received by the 81341 and 81342 while a command is
already in progress receive a NAK to prevent spurious operation. The master is no
longer expected to poll the CMD register to prevent overwriting the current command
in progress prior to issuing further writes. The SMBus access is delayed by stretching
Table 547. SMBus Interface Registers for Configuration Space Access
Register
Name and Function
CMD
Command
BYTCNT
Byte Count
ADDR3
Bus Number
a
a. The ADDR3 field is ignored as Bus Number is not applicable for 81341 and 81342.
ADDR2
Device/Function Number.
b
b. Only ADDR2[2:0] are used to select a Function Number. ADDR2[7:3] are ignored as Device Number is not
applicable to 81341 and 81342.
ADDR1
Extended Register Number — only bits [3:0]. The extended register allows access
to 4-KByte configuration space.
ADDR0
Register Number — offset into function configuration space
DATA3
Data[31:24] — fourth byte of data.
DATA2
Data[23:16] — third byte of data.
DATA1
Data[15:8] — second byte of data.
DATA0
Data[7:0] — first byte of data.
STS
Status, only for reads.
Table 548. SMBus Interface Registers for Memory Space Access
Register
Name and Function
CMD
Command
BYTCNT
Byte Count
ADDR3
Destination Memory.
a
a. The ADDR3 field is ignored on 81341 and 81342 as only the Memory-Mapped Register block are accessible as
a memory space.
ADDR2
Address Offset — bits[23:16].
b
b. Only ADDR2[2:0] are used on 81341 and 81342. ADDR2[7:3] are ignored as the Memory-Mapped Register
Block only occupies 512 KBytes of memory space.
ADDR1
Address Offset — bits[15:8].
ADDR0
Address Offset — bits[7:0].
DATA3
Data[31:24] — fourth byte of data.
DATA2
Data[23:16] — third byte of data.
DATA1
Data[15:8] — second byte of data.
DATA0
Data[7:0] — first byte of data.
STS
Status, only for reads.