Data Exchange
2-2
USS Master Implementation
General Information
The USS protocol (Universal Serial Interface Protocol), defines an access technique according to the
Master-Slave principle for communication via a serial RS-485 based communication bus. The protocol
includes fixed- or variable frame length, cyclic, acyclic and point-to-point communications. The gateway
communicates according to a subset of the protocol, implementing support for cyclic communication
with fixed frame lengths.
All PKW and PZD data is exchanged transparently. This means that the parameter access protocol used
to access PKW data, if required, must be implemented entirely on the PLC side.
Configuration
The gateway can be configured solely using the PROFINET Configuration Tool, e.g. Step 7. No local
configuration tools or settings are required.
See also...
Operation
The gateway will only poll slaves marked as ‘Operational’ in the internal scanlist. Each time a bus cycle
is completed, the gateway checks the status of slaves previously marked as ‘Non-Operational’ and up-
dates the scanlist for the next cycle as necessary.
The status of each individual USS slave can be read in its’ corresponding Slave Status Register.
See also...
• 2-3 “Slave Status Register”
• 4-5 “Slave Diagnostics” (4-5 “Slave Diagnostics”)
