Network Design Considerations
2-2 SIMATIC TIWAY I Series 500 NIM User Manual
2.1 TIWAY I Network Configuration
TIWAY I is a multi-drop communication network which consists of a main
trunk cable (the “spine”) and dropline cables. The network can connect up to
254 secondaries (e.g., Series 500 controllers) to a host computer. The Series
500 NIM provides the interface to the network host, enabling the host and
the controller to communicate with each other.
The following signal-transmission media are supported by TIWAY I:
•RS-232-C/423 dedicated lease-line modem interface in which no dial-up
is necessary, providing extended (cross-continental) geographic
coverage.
•RF or short-haul modem link-ups (cross-plant or cross-town coverage).
•Siemens Local Line (up to 25,000 feet).
NOTE: Media redundancy is supported for RS-232-C and Local Line NIMs.
TIWAY I does not, however, directly support dial-up modems which require
Modem Control Commands for communication switchover. This can be done,
but specific equipment is required to dial the remote number from the host
device.
In order to achieve true redundancy, you must have a completely redundant
network (network trunk lines and drop lines).
The selection of the network communication media depends primarily upon
the geographic distance to be spanned. The main TIWAY I trunk, called the
Local Line, can be up to 10,000 feet long (25,000 feet depending on system
loading and baud rate selection), and can have up to 254 droplines. Each
dropline can be up to 100 feet long. For distances exceeding 25,000 feet,
RS-232-C/423 media interfaces and modems should be used.
NOTE: The proper installation of a communication network requires careful
planning and design. If you need assistance, a free site survey is available
from Siemens. Simply fill out and return the enclosed “TIWAY I Network
Evaluation Form” (Appendix D).
Also included with this manual is a “TIWAY I Network Configuration Data
Sheet” (Appendix C). This will assist you in maintaining a complete,
up-to-date record of the configuration of your network, which is particulary
important if you are using several different types of secondaries.
Communication
Media