Library Of Uss Instructions - Siemens SIMATIC S7-1200 Manual

6.2.2

Library of USS instructions

The USS library supports the USS protocol and provides the functions that are specifically
designed for communicating with drives over the RS485 port of a CM module. You can
control the physical drive and the read/write drive parameters with the USS library. Each
RS485 CM supports a maximum of 16 drives.
● The USS_PORT instruction handles actual communication between the CPU and all the
● The USS_DRV instruction accesses a specified drive on the USS network. The input and
● The USS_RPM and USS_WPM instructions read and write the operating parameters of
An instance DB contains temporary storage and buffers for all of the drives on the USS
network connected to each CM module. The USS instructions for a drive use the instance
DB to share the information.
Execute the USS_PORT from a time-delay interrupt OB to prevent drive timeouts and keep
the most recent USS data updates available for USS_DRV calls.
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drives attached to one CM. Insert a different USS_PORT instruction for each CM in your
application. Ensure that the user program executes the USS_PORT instruction fast
enough to prevent a communication timeout by the drive. Use the USS_PORT instruction
in the program cycle or any interrupt OB.
output parameters of the USS_DRV instruction are the status and controls for the drive. If
there are 16 drives on the network, your program must have at least 16 USS_DRV
instructions, with one instruction for each drive. Ensure that the CPU executes the
USS_DRV instruction at the rate that is required to control the functions of the drive. Use
the USS_DRV instruction only in the program cycle OB.
the remote drive. These parameters control the internal operation of the drive. See the
drive manual for the definition of these parameters. Your program can contain as many of
these instructions as necessary. However, only one read or write request can be active
for any one drive at any given time. Use the USS_RPM and USS_WPM instructions only
in a program cycle OB.
The USS_DRV instruction exchanges data with the drive, by
creating request messages and interpreting the drive response
messages. All of the USS instructions associated with one USS
network and CM must use the same instance DB.
Use a separate USS_DRV instruction for each drive.
The USS_PORT instruction handles communication over the USS
network. Typically, there is only one USS_PORT instruction for each
CM, and the USS_PORT instruction handles the transmission to or
from a single drive.
The USS_RPM instruction reads a parameter from the drive.
Execute the USS_RPM from the program cycle OB.
The USS_WPM instruction modifies a parameter in the drive.
Execute the USS_WPM from the program cycle OB.
The "EEPROM" parameter controls the writing of the data to the
EEPROM. To extend the service life of your EEPROM, Use the
"EEPROM" parameter to minimize the number of EEPROM write
operations.
Easy to communicate between devices
6.2 PtP, USS, and Modbus communication protocols
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