Guidance for implementing zone operations

PMBus Revision 1.3 includes new enhancements called Zone Write and Zone Read. The zone operations bring an important, and powerful, new functionality to PMBus systems. With a single transaction zone commands provide the ability to read from or to write to all of (or a subset thereof) a system’s devices, including any pages within those devices. Implemented on top of the latest SMBus 3.0 [R03] transport specification operating at up to 1MHz clock, zone commands provide for faster transactions while maintaining backward compatibility with the older PMBus 1.2 protocol.

The Zone Read command enables a fast, prioritised response to a query of any data. For example, a Zone Read operation can be used to discover all of the devices attached to a PMBus in one transaction - something that previously could require up to 255 bus operations. Further, Zone Read operations offer improved methods of retrieving system information and provides a means to receive the information of highest priority to the master first.

The application note includes six detailed examples of the use of Zone Read commands. These include Discovering Zone Active Devices in a System, Priority-Based Fault Reporting and Fault Handling, Highest Data Value Request, Fast Telemetry, Priority-Based Telemetry and Reconfigurable Sequencing Based on the Power Good Signal.

Conversely, the Zone Write command provides a solution for synchronised data execution by offering a way to send commands to some or all of the devices on a PMBus in a simple, short transaction. The application note provides three examples of Zone Write commands comprised of Synchronizing Device Turn On and Turn Off, Simultaneous Output Voltage Margin and Simultaneous Configuration Storage.

The Application Note, ‘AN001: Using the ZONE_READ and ZONE_WRITE Protocols’, is free and can be downloaded from the technical section of the pmbus.org website.