User`s guide

Chapter 3 - Receiver Descriptions
Exclusive-Or (XOR) Checksum creation
In Motorola binary mode a checksum must be included with every command to the receiver.
Conversely, all messages from the receiver include a checksum that may be used to verify the
contents of the message.
An example message is used to illustrate the procedure.
Command name: 12 Channel Position/Status/Data Output Message
Command in Motorola binary format: @ @ H a m C < C R > < L F >
In this message, ‘m’ indicates the response message rate (i.e. 1 = once per second, 2 = once
every two seconds, etc.), and ‘C’ is the checksum. In calculating the checksum, only the ‘H', 'a',
and 'm’ characters are used. The Exclusive-Or (XOR) operation yields a one if only one of the bits
is a one. Setting ‘m’ to ‘1’ (or 0x01 in hex), we have the following:
Character Hexadecimal Binary
H 0x48 01001000
a 0x61 01100001
XOR of 0x48 and 0x61: 0x29 00101001
m 0x01 00000001
XOR of 0x24 and 0x01: 0x28 00101000
The final checksum would then be '0x28' in hexadecimal. The complete command
would then be as follows:
Message format @ @ H a m C <CR> <LF>
Hexadecimal: 0x40 0x40 0x48 0x61 0x01 0x28 0x0D 0x0A
ASCII: @ @ H a ^A ( ^M ^J
To enter this command using the WinOncore12 software, one would open the <Msg> window and
type: @@Ha01<Enter> on the command line.
Note: Within the WinOncore12 software, characters beyond the fourth character are treated as
hexadecimal numbers, the checksum is computed automatically, and the <CR><LF> pair is
automatically appended to the command.
The receiver will now output the standard 12 Channel Position/Status/Data message once every
second.
Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05
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