As shown in the table below, the maximum length of a network segment is determined by two factors: isolation (using an RS-485 repeater) and baud rate.
Isolation is required when you connect devices at different potentials. Different reference potentials can exist when grounds are physically separated by a long distance. Even over short distances, load currents of heavy machinery can cause a difference in ground potential.

Baud Rate	Non-Isolated CPU Port	CPU Port with Repeater or EM 277
9.6 kbaud to 187.5 kbaud	50 m	1000 m
500 kbaud	Not supported	400 m
1 Mbaud to 1.5 Mbaud	Not supported	200 m
3 Mbaud to 12 Mbaud	Not supported	100 m

** The maximum distance allowed without using an isolator or repeater is 50 m. You measure this distance from the first node to the last node in the segment.

S7-200 networks use the RS-485 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 W/km
Effective capacitance	30 pF/m
Nominal impedence	Approximately 135 W to 160 W (frequency = 3MHz to 20 MHz)
Attuenuation	0.9 dB/100 m (frequency=200 kHz)
Cress-sectional core area	0.3mm2 to 0.5 mm2
Cable diameter	8 mm +0.5 mm

Connector Pin Assignments

The communication ports on the S7-200 CPUs are RS-485 compatible on a nine-pin subminiature D connector in accordance with the PROFIBUS standard as defined in the European Standard EN 50170. The table below shows the connector that provides the physical connection for the communication port and describes the communication port pin assignments.

	Pin Number	Signal	Port 0/Port 1
	1	Shield	Chassis ground
	2	24V Return	Logic common
	3	RS-485 Signal B	RS-485 Signal B
	4	Request-to-send	RTS(TTL)
	5	5V Return	Logic common
	6	+5V	+5V, 100W series resistor
	7	+24V	+24V
	8	RS-485 Signal A	RS-485 Signal A
	9	Not applicable	10-bit protocol select (input)
	Connector shell	Shield	Chassis ground