Metrohm 781 pH/Ion Meter: Operation via RS-232 - Manual (Page 27)

3 RS232 interface properties
780/781 pH/Ion Meter - Operation via RS232
25
3.3 Pin assignment
RS232C Interface
Transmitted Data (TxD).
If no data are transmitted, the line is held in the “ON”
condition. Data will only be sent when CTS is in the ”ON”
condition.
Received Data (RxD)
Request to Send (RTS)
ON condition: pH/Ion Meter is ready to send data.
Clear to Send (CTS)
ON condition: Remote station is ready to receive data.
Signal ground (GND)
Data Terminal Ready (DTR)
ON condition: Instrument is ready to receive data.
Protective earthing
Direct connection from cable plug to the protective ground of the
instrument.
Polarity allocation of the signals
-
Data lines (TxD, RxD)
voltage negative (<-3 V): signal state ”ON”
voltage positive (>+3 V): signal state ”ZERO”
- control or message lines (CTS, RTS, DTR)
voltage negative (<-3 V): OFF state
voltage positive (>+3 V): ON state
In the transitional range from +3 V to -3 V the signal state is undefined.
Driver according to EIA RS232C specification.
Receiver according to EIA RS232C specification.
Pin 4
Data Terminal Ready
Pin 5
Signal Ground
Pin 8
Clear To Send
Pin 7
Request To Send
Pin 2
Received Data
Pin 3
Transmitted Data