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IDT SMBus Interfaces
Notes
PES48H12G2 User Manual
Bit
Name
Field
0
END
1
START
4:2
FUNCTION
6:5
SIZE
7
PEC
Table 13.13 Slave SMBus Command Code Fields
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. Since the format of these transactions is
different. They will be described individually in the following sections. 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.
CSR Register Read or Write Operation
Table 13.14 indicates the sequence of data as it is presented on the slave SMBus following the byte
address of the Slave SMBus interface.
Byte
Field
Position
Name
0
CCODE
1
BYTCNT
2
CMD
Table 13.14 CSR Register Read or Write Operation Byte Sequence (Part 1 of 2)
Description
End of transaction indicator. Setting both START and END signi-
fies 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.
Start of transaction indicator. Setting both START and END signi-
fies 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.
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
This field encodes the data size of the SMBus transaction.
0 - Byte
1 - Word
2 - Block
3 - Reserved
This bit controls whether packet error checking is enabled for the cur-
rent SMBus transaction.
0 - Packet error checking disabled for the current SMBus transaction.
1 - Packet error checking enabled for the current SMBus transaction.
Command Code. Slave Command Code field described in Table
13.13.
Byte Count. The byte count field is only transmitted for block type
SMBus transactions. SMBus word and byte accesses do not contain
this field. The byte count field indicates the number of bytes following
the byte count field when performing a write or setting up for a read.
The byte count field is also used when returning data to indicate the
number of following bytes (including status). Note that the byte count
field does not include the PEC byte if PEC is enabled.
Command. This field encodes fields related to the CSR register read
or write operation.
13 - 15
Description
April 5, 2013
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