Siemens SIMATIC S7 - Specifications for RS485 Cable; Connector Pin Assignments

Communication
8.6 RS485
S7-200 SMART
460 System Manual, V2.3, 07/2017, A5E03822230-AF
8.6.5.4
Specifications for RS485 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
8.6.5.5
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 output, 100 Ω series resistor
7
+24 V
+24 V output
8
RS485 Signal A
RS485 Signal A
9
Not applicable
Programmer detection (input)
1
Connector
shell
Shield Chassis ground
1
The CPU utilizes pin 9 of the RS485 connector to detect when a USB-PPI cable is connected. The
check for USB-PPI cables is only done on the CRs models. The ST and SR models ignore the
state of pin 9. Ensure that any cables used for Freeport do not connect to pin 9 for the CRs mod-
els.