The input/output scanner is used, periodically, to read or write remote inputs/outputs on the Ethernet network without specific programming. The I/O scanner is configured with Control Expert.
This service comprises the following essential elements:
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a read zone which groups together all the values of remote inputs
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a write zone which groups together all the values of remote outputs
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scanning periods which are independent of the PLC cycle and are specific to each remote device
Scanning is only performed when the PLC is in Run mode.
This service operates with all devices supporting Modbus communication on the TCP/IP profile in server mode.
The exchange mechanism, which is transparent to the user, is carried out with the following requests:
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read requests
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write requests
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read and write requests
NOTE: If you use I/O scanning with gateway/bridge devices, select the check box in the Gateway/Bridge Devices column in the I/O scanner screen, as shown in the following illustration.
The following diagram shows how the scanning of remote inputs/outputs works.
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As soon as the PLC switches to Run mode, the module opens up one connection for each scanned device (one connection for each line entered in the table of scanned elements).
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Then the module periodically reads inputs words, and periodically writes output words for each device.
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If the PLC switches to Stop mode, the connections to each device are closed.
The I/O scanning service functionality is used to:
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manage the connection with each remote device (one connection per device scanned)
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scan the inputs/outputs of the device using Modbus read/write requests on the TCP/IP profile
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update the read and write zones in the application memory
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refresh the status bits for each remote device
Each I/O scanner device can be enabled/disabled.
NOTE: These bits show whether the module's input/output words have been refreshed.
