Datasheet
Interfaces
Intel
®
Xeon
®
Processor C5500/C3500 Series
Datasheet, Volume 1 February 2010
94 Order Number: 323103-001
Every configuration read or write first consists of an SMBus write sequence which
initializes the Bus Number, Device, and so on. The term sequence is used since these
variables may be written with a single block write or multiple word or byte writes. Once
these parameters are initialized, the SMBus master can initiate a read sequence (which
performs a configuration register read) or a write sequence (which performs a
configuration register write).
Each SMBus transaction has an 8-bit command the master sends as part of the packet
to instruct the IIO on handling data transfers. Command format is illustrated in
Table 49 and subsequent bulleted list of sub-field encodings.
• The Begin bit indicates the first transaction of the read or write sequence. The
examples found in Section 2.3.9.1, “SMBus Configuration and Memory Block-Size
Reads” on page 99 through Section 2.3.9.7, “SMBus Configuration and Memory
Byte Writes” on page 104 illustrate when this bit should be set.
• The End bit indicates the last transaction of the read or write sequence. The
examples in Section 2.3.9.1, “SMBus Configuration and Memory Block-Size Reads”
on page 99 through Section 2.3.9.7, “SMBus Configuration and Memory Byte
Writes” on page 104 best describe when this bit should be set.
• The MemTrans bit indicates the configuration request is a memory mapped
addressed register or a PCI (bus, device, function, offset) addressed register. A
logic 0 will address a PCI configuration register. A logic 1 will address a memory
mapped register. When this bit is set it will enable the designation memory address
type.
• The PEC_en bit enables the 8-bit packet error checking (PEC) generation and
checking logic. For the examples below, if PEC was disabled, then there would be
no PEC generated or checked by the slave.
• The Internal Command field specifies the internal command to be issued by the
SMBus slave. The IIO supports dword reads and byte, word, and dword writes to
configuration space.
• The SMBus Command field specifies the SMBus command to be issued on the bus.
This field is used as an indication of the length of transfer so that the slave knows
when to expect the PEC packet (if enabled).
Table 49. SMBus Command Encoding
76 5 4 3:2 1:0
Begin End MemTrans PEC_en
Internal Command:
00 - Read DWord
01 - Write Byte
10 - Write Word
11 - Write DWord
SMBus Command:
00 - Byte
01 - Word
10 - Block
11 - Reserved.
Block command is selected.