The S7-400 backplane bus is a serial data bus via which the CP 440 communicates with the
modules of the programmable controller.
1.4 Features of the X27 (RS 422/485) Interface
Denition
The X27 (RS 422/485) interface is a voltage-dierence interface for serial data transmission in
compliance with the X27 standard.
Properties
The X27 (RS 422/485) interface has the following attributes and is in compliance with the
following requirements:
• Type: Dierential voltage interface
• Front connector: 15-pin sub-D female with screwed interlock
• Max. transmission rate: 115.2 Kbps
• Max. cable length: 1200 m at 19200 Bps
• Standard: DIN 66259 Parts 1 and 3, EIA-RS 422/485, CCITT V.11
• Degree of protection: IP 00
Note
With the RK 512 and 3964(R) protocols, the X27 (RS 422/485) interface submodule can only be
used in four-wire mode.
Cables
Siemens oers standard cables in various lengths for point-to-point connection between the
communication processor and a communication partner.
For order information and the length of standard cables are listed in the appendix
"AUTOHOTSPOT".
Fabricating Your Own Cables
If you are fabricating your own cables, there are a few points to take into consideration. The
appendix "AUTOHOTSPOT" of this manual contains information about this topic as well as the pin
assignment of the sub D male connector and the wiring diagrams.
Product Description
1.4 Features of the X27 (RS 422/485) Interface
Point-to-point connection CP 440 Installation and Parameter Assignment
16 Equipment Manual, 03/2022, A5E00057742-AE
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