Message Structure - ashtech DG16 Reference Manual

As with the other query commands, the port designator (B) is optional. If a port is
not specified, the receiver sends the response to the current port.

Message Structure

Real-time messages are output in binary format:
HEADER,MESSAGE ID,DATA + CHECKSUM<CR><LF>
The header field always contains $PASHR. The message identifier field contains
the three-character message identifier (MBN, PBN, SAL, etc.) and is followed by
a field containing the binary data string. The header, identifier, and data string fields
are comma delimited. Depending on the message selected, the checksum is
contained in the last one or two bytes of the binary data string. All real-time
messages are terminated with a Carriage Return/Line Feed <CR><LF> delimiter.
The MBN message is output:
$PASHR,MPC,<Binary Data String + Checksum><CR><LF>
The general format for the set command to enable or disable output of raw data
messages is $PASHS,RAW,s1,c1,s2 where s1 is the three-character message
identifier, c1 is the port designator, and s2 is ON or OFF. The port designator is a
required parameter in enabling or disabling the output of raw data messages.
Checksum
There are three different algorithms used in the checksum calculation, one for text
messages and two for binary messages:
• Text Messages:
• The hexadecimal checksum is computed by exclusive-O-Ring all of
the bytes in the message between, but not including, the $ and the *
The result is *hh where h is a hex character.
• Binary Messages:
• The checksum for all binary messages except MCA is computed by
breaking the structure into 20 unsigned shorts, adding them together,
and taking the least significant 16 bits of the result.
• The checksum for the MCA message is computed by a
bytewise exclusive OR (XOR) of all bytes from sequence tag (just
after header) to the byte before the checksum.
All bytes are in MC6800 order: most significant byte first (IBM PC uses Intel order: least significant
byte first).
186 DG14 and DG16 Board & Sensor Reference Manual