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TIWAY I Network Configuration (continued)
Timimg
Considerations
2-4
Network Design Considerations
The basic difference in the NIM models is the configuration of the media
interface cards. Examples of the possible application of the different models
are as follows:
If you want media redundancy for a dedicated line (lease-line) modem,
or an RF (short-haul) modem, use PPX:500–5040 which supports
RS-232-C/423 on both Port A and Port B.
If you want media redundancy for a Local Line installation, use
PPX:500–5039 which supports Local Line on both ports.
If you use the Series 500 NIM with a dedicated short-haul RF modem, the
NIM has a one-second time-out between the transmission of its RS-232-C
Request to Send (RTS) and the RS-232-C Clear to Send (CTS) response.
This time-out value is set at one second to enable the RF device to switch
from receive to transmit without losing access to the transmission media.
NOTE: This extended time-out feature is an important consideration when
selecting a TIWAY I-compatible RF Modem. Transmitter/Receiver
turnaround time must be less than the one-second network time-out.
An additional half-second delay from Clear to Send (CTS) to start of
transmission can be added by setting the Keydelay Switch to the OPEN
(left) position. This may be required to allow the transmitter to reach full
power before start of transmission. There is also a one-second wait period
for DCD to turn off in a half-duplex modem.
SIMATIC TIWAY I Series 500 NIM User Manual
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