Siemens SIMATIC ET 200AL, System Manual

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Interrupts/diagnostic messages/diagnostics
6.3 Diagnostics performed at startup
Digital I/O module F-DI 4+F-DQ 2x24VDC/2A, 4xM12 (6ES7146-5FF00-0BA0)
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Equipment Manual, V1.0, 05/2021, A5E51082342-AA
The F-DI 4/F-DQ 2 Fail-Safe module executes tests for its digital outputs of the P- and
M-switches as defined by your configured parameters for "Maximum readback time" and
"Maximum readback time switch on test" after receiving configuration parameters from the
fail-safe CPU at power-up. P- and M-switch ON tests are sequenced so that normally or in the
presence of a single detected fault, there is no complete PM circuit to energize the load.
The F-DI 4/F-DQ 2 Fail-Safe module executes tests for its digital inputs of the sensor supply at
power-up, including ON and OFF pulses, whether or not you have enabled the sensor supply
or short-circuit testing in your configuration. If your configuration includes short-circuit
testing, the module also executes a short-circuit test according to your configured parameters
after receiving the parameters from the fail-safe CPU at power-up.