W83791G Datasheet, PDF (21/99 Pages) Winbond – Winbond H/W Monitoring IC

W83791D/G
6.4 Address Resolution Protocol (ARP) Introduction
As the W8791D/G is a slave device existing on the System Management Bus, it must have a unique
address to prevent itself from conflicting with the other devices existing on the same bus. In order to
solve the problem of address conflicts, SMBus version 2.0 introduces the concept of dynamically
assigned address called Address Resolution Protocol (ARP). By such mechanism, each device
existing on the SMBus will be given a unique slave address if it is a ARP-capable device. Thus, to
meet the new spec, W83791D/G uniquely provides ARP compliant function to acquire a unique slave
address.
The typical process of ARP contains several steps, including Prepare to ARP, Reset Device, Get
UDID, Assign Address, and so on. Whenever the slave device accepts the command of ARP master,
it must reply an Acknowledgement to the ARP master, thus the ARP master is able to carry on the
next step. In order to provide a mechanism to isolate device for the purpose of address assignment,
each device must implement a unique device identifier (UDID). The UDID is a 128-bit number
comprised of several field, including Device Capabilities, Version Revision, Vendor ID, Device ID,
Interface, Subsystem Vendor ID, Subsystem Device ID, and Vendor Specific ID. After the UDID of the
device is sent to the ARP master, the ARP master will then assign a random address not in the Used
Address Pool to the device
Generally speaking, there are eleven possible commands to read /write the data of SMBus device,
and a slave device may use any or all of the eleven protocols to communicate. These protocols are
Quick Command, Send Byte, Receive Byte, Write Byte, Write Word, Read Byte, Read word, Process
Call, Block Write, and Block Write-Block Read Process Call. W83791D/G itself supports the Block
Write-Block Read Process with PEC to communicate with ARP Master. Following is a description of
the SMBus packet protocol diagrams element key. Not all protocol elements will be present in every
command, that is, not all packets are required to include the Packet Error Code.
1-bit 7
1 18
18
1
1-bit
S
Slave Address Wr A ^Command A PEC A
P
S
Sr
Rd
Wr
A
P
PEC
Start Condition
Repeated Start Condition
Read (bit value of 1)
Write (bit value of 0)
Acknowledge (this bit position may be ‘0’ for
an ACK or ‘1’ for a NACK)
Stop Condition
Packet Error Code
Master-to-Slave
Slave-to-Master
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Publication Release Date: April 14, 2006
Revision 1.1