The Benefit Of Time-Stamping Digital I/O; The Ethercat Data Transfer In Cycle Base - Advantech AMAX-5000 Series User Manual

7.1

The Benefit of Time-stamping Digital I/O

7.1.1

The EtherCAT data transfer in cycle base

For the standard EtherCAT digital I/O module, PDO data is transferred cyclically, and
the digital signal state is detected or set at a specific time in the cycle, which means
the response of the I/O is restricted by the EtherCAT cycle time. There will be some
limitations for both digital input and digital output in some application cases.
Take digital input as an example, if an external sensors response time is shorter than
the EtherCAT cycle time, the input signal may not be detected. As shown below, if the
EtherCAT cycle time is 1ms, and the sensor's input signal is 200µs for example, the
sensors state change may be lost in this application (first pulse in the figure). Only
the digital status at the moment of PDO data transfer can be detected (second pulse
in the figure).
Figure 7.1 Standard Digital Input Module Signal Acquisition
Take digital output as another example, if two digital output modules are distributed to
two different stations, when the MDevice sets an output signal to both modules, the
actual output will have little time difference between two modules as shown in the fig-
ure below. Even though the time difference is smaller than a cycle time, it can be crit-
ical especially on the application which needs synchronized signal output.
Figure 7.2 Standard Digital Output Module (SM mode)
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