Omega A2400 User Manual
Page 25
Command Set 4-4
interprets a command, it looks for the two extra characters and assumes that
it is a checksum. If the checksum is not present, the module will perform the
command normally. If the two extra characters are present, the module will
calculate the checksum for the message. If the calculated checksum does
not agree with the transmitted checksum, the module will respond with a
‘BAD CHECKSUM’ error message and the command will be aborted. If the
checksums agree, the command will be executed. If the module receives a
single extra character, it will respond with a ‘SYNTAX ERROR’ and the
command will be aborted. For example:
Command:
$1WE
(no checksum)
Response:
*
Command:
#1WEF0
(with checksum)
Response:
*
Command:
$1WEF1
(incorrect checksum)
Response:
?1 BAD CHECKSUM
Command:
$1WEF
(one extra character)
Response:
?1 SYNTAX ERROR
Response Checksums
If the long form ‘#’ version of a command is transmitted to a module, a
checksum will be appended to the end of the response. For example:
Command:
$1RD
(short form)
Response:
*+99999.99
Command:
#1RD
(long form)
Response:
*1RD+99999.99D9
Checksum Calculation
The checksum is calculated by summing the hexadecimal values of all the
ASCII characters in the message. The lowest order two hex digits of the sum
are used as the checksum. These two digits are then converted to their
ASCII character equivalents and appended to the message. This ensures
that the checksum is in the form of printable characters.