Overview Of Modem Instructions And Restrictions - Siemens Simatic S7-200 System Manual

S7-200 Programmable Controller System Manual

Overview of Modem Instructions and Restrictions

The Modem Expansion wizard makes controlling the Modem module easier by creating unique instruction
subroutines based on the position of the module and configuration options you selected. Each instruction
is prefixed with a "MODx_" where x is the module location.
Requirements for Using the EM 241 Modem Module Instructions
Consider these requirements when you use Modem module instructions:
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The Modem module instructions use three subroutines.
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The Modem module instructions increase the amount of memory required for your program by up to
370 bytes. If you delete an unused instruction subroutine, you can rerun the Modem Expansion
wizard to recreate the instruction if needed.
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You must make sure that only one instruction is active at a time.
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The instructions cannot be used in an interrupt routine.
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The Modem module reads the configuration table information when it first powers up and after a
STOP-to-RUN transition. Any change that your program makes to the configuration table is not
seen by the module until a mode change or the next power cycle.
Using the EM 241 Modem Module Instructions
To use the Modem module instructions in your S7-200 program, follow these steps:
1. Use the Modem Expansion wizard to create the Modem module configuration table.
2. Insert the MODx_CTRL instruction in your program and use the SM0.0 contact to execute it every
scan.
3. Insert a MODx_MSG instruction for each message you need to send.
4. Insert a MODx_XFR instruction for each data transfer.
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