Siemens SIMATIC 500 Series Description And Operating Instructions page 7

I/O Ports
SIMATIC 545/555/575 System Manual
For Communication Port 2, the maximum permissible cable length depends
on the type of connection used:
•
The RS-232/RS-423 connection can extend a maximum of 50 feet
(15 m).
•
The RS-422/RS-485 connection can extend a maximum of 3300 feet
(1 km).
The cable installation for RS-485 or RS-422 can include a 120-ohm
termination resistor across the signal conductors at each end of the cable.
The resistor provides a higher noise immunity and better long-distance
communication.
The 545–1104/–1106 and 555 CPUs have two remote I/O ports.
•
The I/O port is a 9-pin female port used to communicate directly with
Series 505 RBCs by means of a shielded, twisted-pair RS-485 cable.
•
The PROFIBUS-DP port is a 9-pin female port used to communicate to
a variety of PROFIBUS-DP slaves and field devices in daisy-chain
fashion across a shielded, twisted-pair RS-485 cable that meets
PROFIBUS standards.
The 545–1103 CPU has the option of a PROFIBUS-DP port if you install the
PPX:505–CP5434–DP annex card.
Installing 505 System Hardware
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