Vaisala PTB220 - Manual (Page 105)

A PPENDIX I ________________________________________________________________ CHE CKSUM
V AISALA _________________________________________________________________________ 99
APPENDIX I CHECKSUM
With a CHECKSUM form the user can check that the data sent by the
barometer has not changed in transfer line. The CHECKSUM format can
be output with 4 (CS4) or 2 (CS2) hex numbers. The PTB220
calculates the checksum value of all the numbers set before the
parameter CS4/CS2.
>form<cr>
4.2 P " " CS4 #r#n
?
>
>send<cr>
994.16 017B
>
(Please note, there is a space between P and " "-marks)
In following there is an example of checksum calculation of number
1010.09.
1 31 hex
0 30 hex
1 31 hex
0 30 hex
. 2E hex
0 30 hex
9 39 hex
20 hex (space)
179 hex (sum of hex values)
CS4 0179
CS2 79