Geysitech (Bayern-Hessen) Protocol
Block Checksum <BCC>
Thermo Fisher Scientific
Model 49
i
Instruction Manual
D-3
Block Checksum
<BCC>
The block checksum is calculated beginning with a seed value of 00000000,
binary (0x00), and bitwise exclusive ORing with each of the characters of
the command string (or response) including the framing characters <STX>
and <ETX>. The checksum works as an error check. The command
terminator determines the presence or absence of <BCC>.
If a command is terminated by <ETX> then the next two characters are the
checksum, if the command is terminated with <CR> no checksum is
attached
The block checksum is represented by two characters, which represent a 2
digit hex number (1byte). (e.g. 1 byte 0xAB hex checksum will be
represented by the two characters ‘A’ & ‘B’)
The checksum is referred to as <BCC> throughout this document.
Geysitech Commands
The following commands are supported by the Geysitech protocol:
•
Instrument Control Command (ST)
•
Data Sampling/Data Query Command (DA)
Instrument Control
Command (ST)
There are three control commands supported by the Geysitech protocol.
This <control command> is a single letter, which triggers an action in the
instrument. These commands are active only when service mode is inactive
and the zero/span option is present.
Command ‘N’ switches the instrument gas mode to Zero.
For the 49
i
PS, command ‘K’ switches the instrument gas mode to
Level 1.
For the 49
i
, command ‘K’ is not used unless the Sample/Cal option is
present. When the Sample/Cal option is present:
•
If the ozonator is present, command ‘K’ switches the instrument gas
mode to Level 1.
•
If the the ozonator is not present, command ‘K’ switches the
instrument gas mode to Span.
Command ‘M’ switches the instrument gas mode to Sample for the 49
i
and Manual for the 49
i
PS.
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