Signal Description
Every configuration and memory read or write first consists of an SMBus write sequence which
initializes the Bus Number, Device, function number, memory address offset etc. The term
sequence is used since these variables can be initialized by the SMBus master with a single block
write or multiple word or byte writes. The last write in the sequence that completes the
initialization performs the internal configuration/memory read or write. The SMBus master can
then initiate a read sequence which returns the status of the internal read or write command and
also the data in case of a read.
Each SMBus transaction has an 8-bit command driven by the master. The command encodes
information as shown in Table 2-34.
Table 2-34. SMBus Command Encoding
Bit
Description
7
6
5
Begin: When set, this bit indicates the first transaction of the read or write sequence.
End: When set, this bit indicates the last transaction of the read or write sequence.
Memory/Configuration: This bit indicates whether memory or configuration space is being accessed in
this SMBus sequence.
1 = Memory Space
0 = Configuration Space
4
PEC Enable: When set, indicates PEC is enabled for the sequence. When enabled, each transaction in
the sequence ends with an extra CRC byte. The Intel® 6702PXH 64-bit PCI Hub checks for CRC bytes
on writes and generates CRC on reads.
3:2 Internal Command:
00 = Read DWord
01 = Write Byte
10 = Write Word
11 = Write DWord
All accesses are naturally aligned to the access width. This field specifies the internal command to be
issued by the SMBus slave logic to the Intel® 6702PXH 64-bit PCI Hub core.
1:0 SMBus Command:
00 = Byte
01 = Word
10 = Block
11 = Reserved
This field indicates the SMBus command to be issued on the SMBus interface. It is used as an indication
of the length of the transfer so that the slave knows when to expect the PEC packet (if enabled).
2.17.2
Initialization Sequence
All Configuration and memory read and writes are accomplished through SMBus write(s) and later
followed by an SMBus read (for a read command). The SMBus write sequence is used to initialize
the:
• Bus Number,
• Device/Function and
• 12-bit Register Number (in 2 separate bytes on SMBus)
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Intel® 6702PXH 64-bit PCI Hub Datasheet
INTEL [ INTEL ]
