6. Serial line communication
In analog probes, serial line communication is intended for service use only.
HMP60 and HMP110 series probes support 2-wire RS-485 communication. The RS-485
interface is non-isolated and oers a maximum communications rate of 57600 bps.
There is no internal termination for the RS-485 on the probe. Use of termination resistors is not
recommended. If the resistors are used, the possible increase in current consumption should
be taken into account.
6.1 Connecting to serial interface
Connection to the serial interface is through the 4-pin connector on the probe.
For temporary use of the serial interface (for example, calibration), you can use the optional
Vaisala USB cable (item code 219690). Before you can use the cable, you must install the
provided USB driver on your PC.
The Vaisala USB cable is not designed for permanent installations. When using
the USB cable, no separate power unit is needed. The probe is powered through
the USB port.
For permanent interfacing to a host system, use a shielded cable with a threaded connector.
The probe does not echo typed characters back to the terminal screen. To see the commands
you type, you need to enable the "local echo" setting in your terminal program.
A new command cannot be received while the probe is sending data out. Wait until the
instrument has completed its response before entering the next command.
Table 9 Default serial communication settings
Property Description/Value
Baud rate 19200
Parity None
Data bits 8
Stop bits 1
Flow control None
You can change the serial settings and operate in RUN, STOP, POLL, and MODBUS modes.
Chapter 6 – Serial line communication
33
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