W83791D Information Storage Devices, Inc, W83791D Datasheet - Page 21

• Manufacturer Part Number: W83791D
• Description: Hardware Monitor With Speech Synthesizer And Asf Functions
• Manufacturer: Information Storage Devices, Inc

6.4
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 an unique slave
address if it is a ARP-capable device. Thus, to meet the new spec, W83791D uniquely provides ARP compliant
function to acquire an unique slave address.
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
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 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.
Address Resolution Protocol (ARP) Introduction
As the W8791D is a slave device existing on the System Management Bus, it must have a unique address to
The typical process of ARP contains several steps, including Prepare to ARP, Reset Device, Get UDID,
Generally speaking, there are eleven possible commands to read /write the data of SMBus device, and a slave
1-bit
S
7
Slave Address
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
1
Wr A
1
8
Command
14
1
A
8
PEC
Publication Release Date: Aug, 2001
1
A
1-bit
P
W83791D
Preliminary
Revision 0.41