CS120A and CS125 Visibility and Present Weather Sensors
8
4. Communications specification
4.1 Communications electrical specifications
Minimum
Value
Nominal
Value
Maximum
Value
RS-232 Communications
(1)
RS-232 input threshold Low
0.8V
1.5V
-
RS-232 input threshold High
-
2.0V
2.4V
RS-232 input absolute maximum
-15V
-
+15V
RS-232 input resistance
12K
Ω
-
-
RS-232 output voltage low
-
-
0.4V
RS-232 output voltage high (into
3K
Ω
)
4.4V
-
-
RS-485 Communications
RS-485 input threshold voltage
-0.2V
-
+0.2V
RS-485 output (Unloaded)
-
-
5V
RS-485 output (Load 50
Ω
)
2V
-
-
Maximum voltage at any terminal
(2)
-7V
-
+7V
(1)
The RS-232 communications interface will automatically turn itself off when not
transmitting.
(2)
The ground of the sensor and the ground of any RS-485 equipment cannot be further apart
than this voltage. The sensor ground (pin 1) on connector B, see page 18, can be connected
to the ground of the host equipment. This will reduce any parasitic currents.
4.2 Supported data rates and formats
Serial setting
8N1
Supported data rates
•
1200 bps
•
2400 bps
•
9600 bps
•
19200 bps
•
38400 bps - default
•
57600 bps
•
115200 bps
Supported formats
•
RS-232 (Full duplex only), default
•
RS-485 (Half duplex)
•
8 bit data bytes
•
1 stop bit
•
Parity checking is not supported as most communication protocols used
by the CS125 have built in checksums as well as checks that
communications have been understood.