Requirements For Using The Uss Protocol - Siemens Simatic S7-200 System Manual

S7-200 Programmable Controller System Manual

Requirements for Using the USS Protocol

The STEP 7–Micro/WIN Instruction Libraries provides 14 subroutines, 3 interrupt routines, and 8
instructions to support the USS protocol. The USS instructions use the following resources in the S7-200:
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Initializing the USS protocol dedicates Port 0 for the USS communications.
You use the USS_INIT instruction to select either USS or PPI for Port 0. (USS refers to the USS
protocol for SIMOTION MicroMaster drives.) After selecting to use the USS protocol for
communicating with drives, you cannot use Port 0 for any other purpose, including communicating
with STEP 7–Micro/WIN.
During the development of the program for an application using the USS protocol, you should use a
CPU 226, CPU 226XM, or EM 277 PROFIBUS–DP module connected to a PROFIBUS CP card in
your computer. This second communications port allows STEP 7–Micro/WIN to monitor the
application while USS protocol is running.
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The USS instructions affect all of the SM locations that are associated with Freeport
communications on Port 0.
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The USS instructions use 14 subroutines and 3 interrupt routines.
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The USS instructions increase the amount of memory required for your program by up to
3450 bytes. Depending on the specific USS instructions used, the support routines for these
instructions can increase the overhead for the control program by at least 2150 bytes, up to
3450 bytes.
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The variables for the USS instructions require a 400-byte block of V memory. The starting address
for this block is assigned by the user and is reserved for USS variables.
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Some of the USS instructions also require a 16-byte communications buffer. As a parameter for the
instruction, you provide a starting address in V memory for this buffer. It is recommended that a
unique buffer be assigned for each instance of USS instructions.
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When performing calculations, the USS instructions use accumulators AC0 to AC3. You can also
use the accumulators in your program; however, the values in the accumulators will be changed by
the USS instructions.
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The USS instructions cannot be used in an interrupt routine.
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Tip
To change the operation of Port 0 back to PPI so that you can communicate with STEP 7–Micro/WIN,
use another USS_INIT instruction to reassign Port 0.
You can also set the mode switch on the S7-200 to STOP mode. This resets the parameters for Port 0.
Be aware that stopping the communications to the drives also stops the drives.
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