IDT SMBus Interfaces
PES16T4G2 User Manual
5 - 13
January 28, 2013
Notes
CSR Register Read or Write Operation
Table 5.11 indicates the sequence of data as it is presented on the slave SMBus following the byte
address of the Slave SMBus interface.
Table 5.11 indicates the sequence of data as it is presented on the slave SMBus following the byte
address of the Slave SMBus interface. Dword addresses and not byte addresses must be used to access
all visible software registers. ADDRL and ADDUL represent the lower 8-bit of the doubleword system
address and upper 6-bit doubleword system address, respectively. For example, use ADDRU = x00 and
ADDRL = 0x00 to access system address 0x00000 (port 0’s Vendor/Device ID register). Use ADDRU = x00
and ADDRL = 0x01 to access system address 0x00004 (port 0’s Command/Status register).
The format of the CMD field is shown in Figure 5.6 and described in Table 5.12.
Figure 5.6 CSR Register Read or Write CMD Field Format
Byte
Position
Field
Name
Description
0
CCODE
Command Code. Slave Command Code field described in Table
5.10.
1
BYTCNT
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.
2
CMD
Command. This field encodes fields related to the CSR register read
or write operation.
3
ADDRL
Address Low. Lower 8-bits of the doubleword CSR system address
of register to access.
4
ADDRU
Address Upper. Upper 6-bits of the doubleword CSR system
address of register to access. Bits 6 and 7 in the byte must be zero
and are ignored by the hardware.
5
DATALL
Data Lower. Bits [7:0] of data doubleword.
6
DATALM
Data Lower Middle. Bits [15:8] of data doubleword.
7
DATAUM
Data Upper Middle. Bits [23:16] of data doubleword.
8
DATAUU
Data Upper. Bits [31:24] of data doubleword.
Table 5.11 CSR Register Read or Write Operation Byte Sequence
Bit
6
Bit
7
Bit
0
Bit
1
Bit
2
Bit
3
Bit
4
Bit
5
BELL
BELM
WERR
BEUM
BEUU
OP
RERR
0
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