Siemens Simatic S7 Series

Communication
8.6 RS485
S7-200 SMART
402 System Manual, 09/2015, A5E03822230-AC
8.6.4.4
Selection of the network cable
S7-200 SMART CPU networks use the RS485 standard on twisted pair cables. The following
table lists the specifications for the network cable. You can connect up to 32 devices on a
network segment.
Specifications
Description
Cable type
Shielded, twisted pair
Loop resistance
≤115 /km
Effective capacitance
30 pF/m
Nominal impedance Approximately 135 to 160
(frequency = 3MHz to 20 MHz)
Attenuation
0.9 dB/100 m (frequency=200 kHz)
Cross-sectional core area
0.3 mm
2
to 0.5 mm
2
Cable diameter
8 mm +0.5 mm
8.6.4.5
Connector pin assignments
The RS485 communication port on the S7-200 SMART CPUs is RS485-compatible on a
nine-pin subminiature D connector, in accordance with the PROFIBUS standard as defined
in the European Standard EN 50170. The following table shows the connector that provides
the physical connection for the communication port and describes the communication port
pin assignments.
Table 8- 17 Pin assignments for the S7-200 SMART CPU integrated RS485 port (Port 0)
Pin number
Connector
Signal
Integrated RS485 port (Port 0)
1
Shield
Chassis ground
2
24 V Return
Logic common
3 RS485 Signal
B
RS485 Signal B
4 Request-to-
Send
RTS (TTL)
5
5 V Return
Logic common
6
+5 V
+5 V, 100 Ω series resistor
7
+24 V
+24 V
8 RS485 Signal
A
RS485 Signal A
9
Not applicable
10-bit protocol select (input)
Connector
shell
Shield Chassis ground