INFICON Composer Gas Concentration Controller - Manual (Page 145)

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Composer Operating Manual
7.4.1 Structure of a Command Sent to Composer
Length Command [Subcommand] [Program Number] [Data] Checksum
Length is one byte, and does not include the checksum, or the length itself.
Command is one character and represents the major categories of commands.
Many commands are further delimited by sub-commands. See
section 7.4.3 on
page 7-5 .
Subcommand is a further delimiter of some of the commands. Subcommands
are one character. See
section 7.4.3 on page 7-5 .
Program Number is required for all Query and Update commands except Q 17
and U 17. This is a number between 1 and 9 that indicates which of the data
sets is being referred to.
Data are required for some commands. The format of the data is determined by
the specific command. See
section 7.4.3 on page 7-5 .
Checksum is a one byte sum of all the bytes in the command, not including the
length or the checksum itself.