GLOBALSAT TR-203A - Manual (Page 5)

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2 Protocol Summary
2.1 General Format
GS x ,IMEI, [T,S,] Field1,Field2,……,FieldN*Checksum!
Format Description Note
GS x ”GS S ” :Write setting
”GS s ” :Report setting
”GS G ” :Write Geo-fence parameter
”GS g ” :Report Geo-fence parameter
”GS C ” :Action command
”GS r ” :Position and status report (format 0)
”GS h ” :Position and status report (format 1)
Command head
IMEI (The IMEI number) GSM device ID
T ‘ 0 ’ : Middle of message
‘ 1 ’ : Start of message
‘ 2 ’ : End of message
‘ 3 ’ : Start and End of message, i.e., only one
packet for message
Message packet
control
S ‘0’,’1’,’2’,’3’,…,’9’,’10’,’11’,…,’99’ Sequence number
Field Field1 ~ FieldN Refer to “TR-203
configure
parameters” for
detail definition
* * End of field
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.
! ! Message delimiter