Spectracom 8194B, Инструкция по эксплуатации

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Spectracom Corporation 8194B, 8195B, 8197B
GPS Ageless Master Oscillator Instruction Manual 3-15
3.3.5.4 Termination
Switch 10 terminates the RS-485 Receive line with 120 ohms. Place Switch 10 in the
ON position when the unit is installed at the end of the RS-485 bus. Place this switch in
the OFF position when the unit is not the last device on the bus.
3.3.6 RS-485 COM
The RS-485 communication port permits remote configuration control and monitoring of
performance and status. The RS-485 Com port uses a protocol and command set
described in Section 4.3 of this manual. The Com connector pin numbering is shown in
Figure 3-10. Table 3-7 lists the Com pin assignments.
Figure 3-10 RS458 COM Connector
PIN SIGNAL NOTES
1 - Transmit RS-485 A terminal
2 + Transmit RS-485 B terminal
3 - Receive RS-485 A terminal
4 + Receive RS-485 B terminal
5 Ground Cable Shield
6 Ground Cable Shield
Table 3-7 RS-485 COM Pin Assignments
The rear panel DIP-switch selects the RS-485 address and termination as described in
previous paragraphs. Transmitted characters are in ASCII form with a bit structure of 1
start, 8 data, 1 stop and no parity, data rate is 9600 baud.
RS-485 is a balanced differential transmission requiring twisted pair cable. The RS-485
standard defines the A terminal (-) to be negative with respect to the B terminal (+) for a
Binary 1 (MARK or OFF) state. The A terminal (-) is positive to the B terminal (+) for a
Binary 0 (SPACE or ON) state. Figure 3-11 illustrates the relationship between the A
and B terminals for the Transmit and Receive connections.