IDT PCI Express 89HPES32NT24xG2, User Manual, Page: 235 / 744

IDT SMBus Interfaces
PES32NT24xG2 User Manual 12 - 31 January 30, 2013
Notes
The FUNCTION field in the command code indicates if the SMBus operation is a system address
register read/write or a serial EEPROM read/write operation. If a command is issued while one is already in
progress or if the slave is unable to supply data associated with a command, then the command is
NACKed. This indicates to the master that the transaction should be retried.
The format of the CMD field is shown in Table 12.25.
Bit
Fields
Field
Name
Description
0 END End of transaction indicator. Setting both START and END signifies a
single transaction sequence
0 - Current transaction is not the last read or write sequence.
1 - Current transaction is the last read or write sequence.
1 START Start of transaction indicator. Setting both START and END signifies
a single transaction sequence
0 - Current transaction is not the first of a read or write sequence.
1 - Current transaction is the first of a read or write sequence.
4 : 2 FUNCTION This field encodes the type of SMBus operation.
0 - CSR register read or write operation
1 - Serial EEPROM read or write operation
2 through 7 - Reserved
6 : 5 SIZE This field encodes the data size of the SMBus transaction.
0 - Byte
1 - Word
2 - Block
3 - Reserved
7 PEC This bit controls whether packet error checking is enabled for the current
SMBus transaction.
0 - Packet error checking disabled for the current SMBus transaction.
1 - Packet error checking enabled for the current SMBus transaction.
Table 12.24 Slave SMBus Command Code Fields
Bit
Field
Field
Name
Type Description
0 BELL Read/Write Byte Enable Lower. When set, the byte enable for bits [7:0] of the
data word is enabled.
1 BELM Read/Write Byte Enable Lower Middle. When set, the byte enable for bits [15:8]
of the data word is enabled.
2 BEUM Read/Write Byte Enable Upper Middle. When set, the byte enable for bits
[23:16] of the data word is enabled.
3 BEUU Read/Write Byte Enable Upper. When set, the byte enable for bits [31:24] of the
data word is enabled.
4 OP Read/Write CSR Operation. This field encodes the CSR operation to be per-
formed.
0 - CSR write
1 - CSR read
Table 12.25 CSR Register Read or Write CMD Field Description (Part 1 of 2)