IDT SMBus Interfaces
PES16NT2 User Manual
6 - 10
April 15, 2008
Notes
The FUNCTION field in the command code indicates if the SMBus operation is a CSR 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 associ-
ated with a command, the command is NACKed. This indicates to the master that the transaction should be
retried.
CSR Register Read or Write Operation
Table 6.9 indicates the sequence of data as it is presented on the slave SMBus following the byte
address of the Slave SMBus interface.
Bit
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 cur-
rent SMBus transaction.
0 - Packet error checking disabled for the current SMBus transaction.
1 - Packet error checking enabled for the current SMBus transaction.
Table 6.8 Slave SMBus Command Code Fields
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