6402 datasheet(79/250 Pages) INTEL

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Intel® 6400/6402 Advanced Memory Buffer Datasheet

SMBus Interface

7.1.3.1

Configuration Register Read Protocol

Configuration reads are accomplished through an SMBus write(s) and later followed by

an SMBus read. The write sequence is used to initialize the Bus Number, Device,

Function, and Register Number for the configuration access. The writing of this

information can be accomplished through any combination of the supported SMBus

write commands (Block, Word, or Byte). The Internal Command field for each write

should specify Read DWord.

After all the information is set up, the last write (End bit is set) initiates an internal

configuration read. If an error occurs during the internal access, the last write

command will receive a NACK. A status field indicates abnormal termination and

contains status information such as target abort, master abort, and time-outs. The

status field encoding is defined in the following table.

Examples of configuration reads are illustrated below. All of these examples have PEC

(Packet Error Code) enabled. If the master does not support PEC, then bit 4 of the

command would be cleared and there would not be a PEC phase. For the definition of

the diagram conventions below, refer to the SMBus Specification, Rev. 2.0. For SMBus

read transactions, the last byte of data (or the PEC byte if enabled) is NACKed by the

master to indicate the end of the transaction. For diagram compactness, “Register

Number[]” is also sometimes referred to as “Reg Number” or “Reg Num”.

The following example uses byte reads.

Table 7-3.

Status Field Encoding for SMBus Reads

Bit

Description

Reserved

Internal Target Abort

3:1

Reserved

Successful

Figure 7-1. SMBus Configuration Read (Block Write / Block Read, PEC Enabled)

X011_XXX

W A

Cmd = 11010010

X011_XXX

R A

Byte Count = 5

Status

Data[31:24]

Data[23:16]

Data[15:8]

Data[7:0]

X011_XXX

W A

Cmd = 11010010

Byte Count = 4

Reserved

Device/Function

Reg Number[15:8]

Reg Number [7:0]

PEC

A P

PEC

N P

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