Serial line output commands - GMP231

GMP231 User Guide

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Table 1. R command
Syntax Description

Start the continuous outputting of measurement values as an ASCII text string to the serial line.

The probe keeps outputting measurement messages at the interval that has been set with the INTV command until stopped with the S command or with the Esc key.

Example (measurement message in default format):

CO2=  490 ppm
CO2=  490 ppm
CO2=  491 ppm
CO2=  491 ppm
CO2=  491 ppm
Table 2. S command
Syntax Description
S<cr> Stop the continuous outputting that was started with the R command.
CO2= 5.1 %CO2
CO2= 5.0 %CO2
CO2= 5.0 %CO2
Table 3. INTV command
Syntax Description
INTV [n xxx]<cr> Change the output interval of the automatically repeating measurement messages. The measurement messages are repeated in the RUN mode, or after the R command has been given.

Set the output interval.

  • n = interval, range 0 ... 255
  • xxx = unit for interval setting.
    • s = seconds
    • min = minutes
    • h = hours

If you set the interval to 0, the output messages are output as quickly as they are generated, without additional delay.


intv 5 s
Output interval     : 5 S
Table 4. SEND command
Syntax Description
SEND<cr> Output a single measurement message.


CO2=  1702 ppm
Table 5. FORM command
Syntax Description
FORM<cr> Change the measurement message sent by the probe.
FORM /<cr> Reset measurement format to default.
FORM [modifier string]<cr>

modifier string = String of parameters and modifiers that defines the output format, length 1 ... 150 characters. Maximum length may be shorter when text strings are used.

For more information, see Table 6 and Table 7.


Example of default output (continuous output from RUN mode):

CO2=   860 ppm
CO2=   861 ppm
CO2=   861 ppm

Command to set output format as %CO2:

form 3.1 "CO2=" CO2% " " U4 #r #n

Output example:

CO2=  5.1 %CO2 
CO2=  5.1 %CO2 
CO2=  5.0 %CO2 

Command to set output format as CO2 ppm with Modulus-65536 checksum:

form 6.0 "CO2=" CO2 " " U3 " " CS4 #r #n

Output example:

CO2=  3563 ppm 9F
CO2=  3562 ppm 9E
CO2=  3559 ppm A4

Command to set output format as CO2 ppm, with start of text (ASCII character 002) and end of text (003) ASCII codes, and without line feed and carriage return at the end:

form #002 6.0 "CO2=" CO2 " " U3 #003

Output example (ASCII codes not visible here):

CO2=   866 ppm CO2=   866 ppm CO2=   867 ppm CO2=   867 ppm
CO2=   867 ppm CO2=   868 ppm CO2=   868 ppm CO2=   869 ppm
Table 6. Output commands for FORM command
Measured parameter Abbreviation in FORM command
Carbon dioxide in ppm CO2
Carbon dioxide in percent CO2%
Currently used temperature compensation value TCOMP
Currently used pressure compensation value PCOMP
Currently used oxygen concentration compensation value O2COMP
Currently used relative humidity compensation value RHCOMP
Table 7. Modifiers for FORM command
Modifier Description
x.y Length modifier (number of digits and decimal places)
#t Tabulator
#r Carriage-return
#n Line feed
"" String constant, length 1 ... 15 characters
#xxx ASCII code value (decimal) of a special character; for example, #027 for ESC
ADDR Probe address (0 ... 254)
SN Probe serial number
TIME Cumulative operating hours of the probe.
Ux Shows the name of the measurement unit using “x” number of characters. For example, U3 shows the name of the measurement unit with three characters
CS4 Modulus-65536 checksum of message sent so far, ASCII encoded hexadecimal notation
CSX NMEA xor-checksum of message sent so far, ASCII encoded hexadecimal notation