System Management Bus (SMBus) Specification, version 2.

System Management Bus (SMBus) Specification Version 2.0
Referring to the previous flow diagram an ARP-capable device operates as follows:
1. After exiting the power on reset state, a device that supports the Persistent Slave Address (PSA) will
go to step 2 to see if it is valid. If the device does not support the PSA, it will proceed to step 5.
2. A device supporting PSA must check its Address Valid flag which is a non-volatile. If that flag is set
then it has previously received an assigned slave address and proceeds to step 4. If the Address Valid
flag is cleared then it must proceed to step 3
3. Although the device supports the PSA the value is currently invalid. The device must clear the Address
Resolved flag indicating that it has not had its slave address assigned. Proceed to step 6.
4. The device has a valid PSA so it assumes that slave address for now. However, this address has not
been resolved by the ARP Master so the device must clear its Address Resolved flag. Proceed to step
6.
5. The device does not support the PSA so it must clear its Address Valid and Address Resolved flags.
Proceed to step 6.
6. If supported, the device will master the SMBus and send the “Notify ARP Master” command. This will
inform the ARP Master that a new device is present. Proceed to step 7.
7. The device waits for an SMBus packet.
8. Upon receipt of an SMBus packet the device must first check the received slave address against the
SMBus Device Default Address. If there is a match then it proceeds to step 12, otherwise it proceeds to
step 9.
9. The received address is not the SMBus Device Default Address so the packet is potentially addressed
to the device’s core function. The device must check its Address Valid bit to determine whether or not
to respond. If the Address valid bit is set then it proceeds to step 10, otherwise it must return to step 7
and wait for another SMBus packet.
10. Since the device has a valid slave address it must compare the received slave address to its slave
address. If there is a match then it proceeds to step 11, otherwise it must return to step 7 and wait for
another SMBus packet.
11. The device has received a packet addressed to its core function so it acknowledges the packet and
processes it accordingly. Proceed to step 7 and wait for another SMBus packet.
12. The device detected a packet addressed to the SMBus Device Default Address. It must check the
command field to determine if this is the “Prepare To ARP” command. If so, then it proceeds to step
13, otherwise it proceeds to step 14.
13. Upon receipt of the “Prepare To ARP” command the device must acknowledge the packet and make
sure its Address Resolved flag is clear in order to participate in the ARP process. Proceed to step 7 and
wait for another SMBus packet.
14. The device checks the command field to see if the “Reset Device” command was issued. If so, then it
proceeds to step 15, otherwise it proceeds to step 16.
15. Upon receipt of the “Reset Device” command the device must acknowledge the packet and make sure
its Address Valid (if non-PSA) and Address Resolved flags are cleared. This will allow the ARP
Master to re-assign all device addresses without cycling power. Proceed to step 7 and wait for another
SMBus packet.
16. The device checks the command field to see if the “Assign Address” command was issued. If so, then
it proceeds to step 17, otherwise it proceeds to step 19.
17. Upon receipt of the “Assign Address” command the device must compare its UDID to the one it is
receiving. If any byte does not match then it must not acknowledge that byte or subsequent ones. If all
bytes in the UDID compare then the device proceeds to step 18, otherwise it must return to step 7 and
wait for another SMBus packet.
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