Siemens SINAUT ST7 System Manual page 283

RS-232
RS-232 is a standard for serial (i.e. bit-by bit) data transmission with +12 V and -12 V
signals. RS-232 is a Recommended Standard of the Electronic Industries Association. For
the RS-232 interface, 9-pin and 25-pin connections with D-sub connectors are normal.
These are sub-miniature connectors with a D-shaped face.
RS-485
RS-485 is a standard for data transmission with 5 V differential signals. The RS-485
interface uses only one pair of wires and is operated in half duplex. The connection is
multipoint-compliant; in other words, up to 32 subscribers can be connected.
Send buffer
Image memory / send buffer
→
Send buffer principle
If a send message is transmitted using the send buffer principle, each time the message is
transferred to the TIM, it is entered completely in the send buffer. If such a message cannot
(or should not) be transmitted immediately, it may exist more than once in the send buffer.
When it is sent, the message is taken completely from the send buffer and transmitted.
See also → Image memory / send buffer
Setpoint
A setpoint is a selected digital or analog value that is transmitted once after the value has
been set. The entered value is recalculated when necessary. A setpoint is always
transmitted as 1 word. At the receiving end, the setpoint can either the output directly to the
process as an analog signal (for example to an external controller) or the value is made
available to the local program for further processing (setpoint for internal controller, limit
value, threshold value etc.).
Setpoint and command input are interlocked for safety reasons; in other words, a setpoint
input cannot be made at the same time as a command input. In this case, the acquisition
program recognizes an error. Neither the setpoint nor the command are transmitted.
SIM card
(Subscriber Identity Module)
The SIM card is an identification card for a subscriber of a GSM mobile wireless network.
SIMATIC S7
Siemens automation system
Station control system
System Manual, 07/2009, C79000-G8976-C178-07
Glossary
283