Since the software acts so much like a real processor, many users will attempt to force I/O without considering an important fact about emulation: There is no I/O.
Caution: Support for forcing in the software is there for your convenience in an attempt to emulate how the processor will behave. There are differences between how a real processor forces and how the software forces, and you should be aware of those differences. If you are not familiar with forcing in a real processor, see your processor's documentation for information about forcing. Do not rely on your background in forcing in the software when attempting to force I/O in a real processor. Unexpected machine movement could result, causing damage to equipment and injury to personnel.
When you force an input or output in a real processor, the force takes place in the I/O image table, not in the processor data table. Since the software relies on only the data table, forcing does not always work the same way as in a real processor. The following table describes the differences:
This bit type:
|
In this force mode:
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When enabling forces:
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When disabling forces:
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Input
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ON
|
In a real processor, forcing an input ON forces a bit in the I/O image table. When the processor updates the Data Table, the forced bit in the image table appears as ON in the input data table file.
In the software, forcing an input ON sets the address in the data table ON (1) at the beginning of the program scan. The value of the input is still dictated by the ladder program. |
In a real processor, removing or disabling an ON force removes the force and allows the input address value to be dictated by the state of the real I/O.
In the software, removing or disabling an ON force allows the input address value to be dictated by the state of real I/O. Since there is no real I/O, the input remains ON until manually reset to OFF (0). |
OFF
|
In a real processor, forcing an input OFF forces a bit in the I/O image table. When the processor updates the Data Table, the forced bit in the image table appears as OFF in the input data table file.
In the software, forcing an input OFF sets the address in the data table OFF (0) at the beginning of the program scan. The value of the input is still dictated by the ladder program. |
In a real processor, removing or disabling an OFF force removes the force and allows the input address value to be dictated by the state of the real I/O.
In the software, removing or disabling an OFF force allows the input address value to be dictated by the state of real I/O. Since there is no real I/O, the input remains OFF until manually reset to ON (1). | |
Output
|
ON
|
In a real processor, forcing an output ON forces a bit in the I/O image table. Values in the data table are not affected by the force.
In the software, forcing an output ON forces a bit in the I/O image table. Values in the data table are not affected by the force. |
In a real processor, removing or disabling an ON force removes the force and allows the output address value to be dictated by the state of the I/O image table.
In the software, removing or disabling an ON force removes the force and allows the value of the output data table address to be dictated by the ladder program. |
OFF
|
In a real processor, forcing an output OFF forces a bit in the output image table. This causes the output on the real I/O module to turn off. The value in the output data table is not affected by the force.
In the software, forcing an output ON forces a bit in the I/O image table. Values in the data table are not affected by the force. |
In a real processor, removing or disabling an OFF force and allows the value of the output image table address to be dictated by the output data table.
In the software, removing or disabling an OFF force removes the force and allows the value in the output data table to be dictated by the ladder program. |
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