Siemens SIMATIC TIWAY 1 Manual de usuario descargar pdf (Pagina 36)

Network Design Considerations

2-19

TIWAY 1 Ti505 NIM User Manual

2.4.5 Terminating

the Local Line

The

TIW

Y I Local Line is designed to operate with shielded, twisted-pair cable which

has

a characteristic impedance

of 124 ohms. In all configurations, the Local Line must be

properly

terminated at both ends of the trunk to prevent an impedance mismatch

which

could result in signal reflections on the line. Termination is required regardless of the

number

or type of devices attached to the network.

NOTE

In the special case of a PM550 using a CIM as its interface to the net-

work,

see

Appendix A for detailed line biasing and termination instruc

tions,

which vary from those listed here.

Termination

of the Local Line must be at the tap housings at the extreme ends of the net

work

spine, and is accomplished as follows:

The factory-installed termination resistors in the tap housing (see

Figure 5)

are

left in place in the tap housing which is to be used to terminate the

Local

Line.

2. If

the termination resistors are used and the attached TIW

Y I device has a Bias

Switch,

the Bias Switch should be set to the ON position.

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Siemens SIMATIC TIWAY 1 Manual de usuario Pagina 36