Siemens SIMATIC ET 200S Operating Instructions Manual page 160

Glossary
SYNC
This is a control command of the DP master to a group of DP slaves.
With the SYNC control command the DP master orders the DP slave that the DP slave
freeze the states of the outputs to the current value. With the subsequent frames, the DP
slave stores the output data, but the statuses of the outputs remain unchanged.
After each new SYNC control command, the DP slave sets the outputs that it has stored as
output data. The outputs are not cyclically updated again until the DP master sends the
UNSYNC control command.
Technological modules
Modules that are equipped with technological functions, such as counting pulses,
positioning, and controlling stepping motor power units.
Terminal modules
Terminal modules implement the electrical and mechanical connection of the I/O modules
with the interface module and the terminating module.
The inserted I/O module determines the signals at the terminals of the terminal module.
Depending on the selected terminal module only certain terminals are available.
Terminating module
The ET 200S distributed IO system is completed by the terminating module. If you have not
inserted a terminating module, the ET 200S is not ready for operation.
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Operating Instructions, 08/2008, A5E00515771-06
ET 200S