Siemens SIMATIC ET 200S Manual page 562

Glossary
Segment
The bus line between two terminating resistors forms a segment. A segment
contains 0 to 32 ³ bus nodes. Segments can be interconnected by means of
RS 485 repeaters.
SELV
Safety Extra Low Voltage = safety extra-low voltage
Slave
A slave can only exchange data with a ³ master when requested by it to do so. By
slaves we mean, for example, all DP slaves such as ET 200X, ET 200M, ET 200S,
etc.
SSI
The positional information is transferred synchronously on the basis of the SSI
(synchronous serial interface) protocol. The SSI protocol is used with absolute
encoders.
Stationary wiring
All the wiring-carrying elements (terminal modules) are mounted on a rail. The
power and electronic modules are inserted in the terminal modules.
SYNC
This is a control command of the DP master to a group of DP slaves.
By means of the SYNC control command, the DP master causes the DP slave to
freeze the current statuses of the outputs. 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.
Terminating module
The ET 200S distributed I/O system is completed by the terminating module. If you
have not connected a terminating module, the ET 200S is not ready for operation.
Transmission rate
The transmission rate of a data transfer is measured in bits transmitted per
second.
In the case of the ET 200S, transmission rates of 9.6 kbps to 12 Mbps are
possible.
Glossary-6
ET 200S Distributed I/O System
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