GLOBALSAT TR-203A - Manual (Page 29)

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2.10 Checksum
The checksum value is derived by the same method of NMEA standard. It is
calculated by ‘exclusive OR’ the 8 data bits of each character before “*” in the
sentence, but excluding “*”. The hexadecimal value of the most significant and
least significant 4 bits of the result are converted to two ASCII characters (0-9, A-F)
for transmission. The most significant character is transmitted first.
Example1: set the device whose IMEI is 011412000011274, the APN is internet, the user
name and password are not necessary, the server type is TCP, the server IP is
220.128.207.75, the server port number 3000.
The setup command is
GSS,011412000011274,3,1,D1=internet,D2=,D3=,D8=02,E0=220.128.207.75,E1=3000
*5E!
The checksum is 5E.
Example2: Set TR-203 periodic report and ask it to report based on traveled distance
(P3) of 500 meters
The setup command is
GSC,011412000010789,M2(P3=500)*72!
The checksum is 72.
Example3: Set TR-203 parking mode with report interval of 3600 seconds for alert state
(T0), report interval of 30 for alarm state (T1), report’s traveled distance of 700 meters
(T3) and report media (T2) TCP
GSC,011412000010789,M6(T0=3600,T1=30,T2=02,T3=700)*02!
The checksum is 02.