Chapter 4 _________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 103
Usually, PWD32 waits for input from both the RS-232 and RS-485
interfaces. Any character from the RS-232 interface disables the RS-485
communication for 10 seconds or until the line is closed by the operator.
This allows PWD32 control to be transferred from the host computer
(FSC202) to the maintenance terminal.
Transmitted data appears on both interfaces.
Serial Communication Settings
In this FS11P application the default settings of the serial
communications port are as follows:
- 9600 baud
- No parity
- 8 data bits
- 1 stop bit
Serial Transmission RS-232
For the RS-232 communication the Vaisala standard maintenance
terminal cable QMZ101 connects the PWD32 signal wires to a standard
PC/Laptop RS-232 interface sub-D9 connector:
- RS-232 TxD to PC sub-D 3/9
- RS-232 RxD to PC sub-D 2/9
- GND to PC sub-D 5/9
Vaisala recommendation for the maximum length of the RS-232 cable is
50 m. Usually the RS-232 connection can be used with distances up to
100 m without problems, but this cannot be guaranteed.
Any computer equipped with terminal emulation software or a VT 100
compatible terminal with RS-232 serial interface can be used as a
Maintenance Terminal for PWD32.
Serial Multipoint Transmission RS-485
The RS-485 transmission standard allows PWD32 to communicate (half
duplex) with the host computer using a single twisted pair, connecting
also the visibility sensor FSM102 and the optional background luminance
sensor LM21F to the host (FSC202).
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