Siemens 500 NIM - Manual (Page 45)

Installation 3-10 SIMATIC TIWAY I Series 500 NIM User Manual
Setting the Dipswitches (continued)
Synchronous/Asynchronous Selection. Configuration switch 5 selects
synchronous or asynchronous operation for modems. For synchronous
modem communication, the NIM receives the transmit and receive timing
signals from the modem via transmit signal timing element (DB), and
receive signal timing element (DD). If the modem data rate does not match
a TIWAY data rate exactly, the data rate select switches should be set to a
rate that is the next lower data rate from the modem For example, if a
56,000 bps synchronous modem is used, a data rate of 38,400 bps should be
selected on the NIM.
For asynchronous operation, the transmit and receive timing elements are
generated within the NIM. When using the local line medium, this switch
must be in the asynchronous position (to the right, closed, indicates
asynchronous, to the left, open, is synchronous.)
Full/Half Duplex. Configuration switch 6 selects full or half duplex
operation when communicating over an RS-232-C data link. When half
duplex is selected (switch 6 = 0, closed, or to the right) the NIM waits for the
data carrier detect (DCD) control signal from the modem to go inactive
before activating the request to send (RTS) control signal. If full duplex
operation is selected, the timing relationship between DCD and RTS will be
ignored. When the local line communication media is used, this switch is
ignored since no externally supplied communication control signals are
supplied.
X.25/HDLC. Configuration switch 7 selects the communication protocol.
The HDLC protocol is activated when the switch is set to 0. The X.25
protocol is only activated when this switch is set to 1. The X.25 protocol is
not used with the TIWAY I or UNILINK Host Adapter, although it is an
option when communicating with any host supporting this protocol. For a
more detailed description of these protocols, see the SIMATIC TIWAY I
Systems Manual (TIWAY–8101).
NRZ/NRZI. Configuration switch 8 selects the method of data encoding
used on the physical communication medium. The NRZI method of data
encoding provides a mechanism for the proper decoding of received data in
an asynchronous communication environment. In fact, NRZ encoding will
not work satisfactorily except in the case of synchronous RS-232-C
communication. When using Local Line, or asynchronous RS-232-C , NRZI
encoding must be used. Either type of encoding may be used with
synchronous RS-232-C communication.