RoyalTek REB-3000 Operational Manual page 25

RoyalTek RGM-3000/REB-3000
GPS Module Operational Manual)
but operates independently. The byte count
refers to the payload byte length. Likewise,
the check sum is a sum on the payload.
Message Length
The message length is transmitted high
order byte first followed by the low byte.
High Byte
<0x7F>
Even though the protocol has a maximum
length of (2 15 -1) bytes practical
considerations require the SiRF GPS
module implementation to limit this value to
a smaller number. Likewise, the SiRF
receiving programs (e.g., SiRF demo) may
limit the actual size to something less than
this maximum..
Payload Data
The payload data follows the message
length. It contains the number of bytes
specified by the message length. The
payload data may contain any 8-bit value.
Where multi-byte values are in the payload
Input Messages for SiRF Binary Protocol
Note – All input messages are sent in BINARY
format
Table 19 SiRF Messages – Input Message List
Hex
0 x 80
0 x 81
0 x 82
0 x 84
0x 85
0x 86
0 x 88
0 x 89
0 x 8A
0 x 8B
0 x 8C
0 x 8D
0 x 8E
0 x 8F
0 x 90
0 x 91
Low Byte
Any value
ASCII
128 Initialize Data Source
129 Switch to NMEA Protocol
130 Set Almanac
132 Software Version
133 DGPS Source Control
134 Set Main Serial Port
136 Mode Control
137 DOP Mask Control
138 DGPS Mode
139 Elevation Mask
140 Power Mask
141 Editing Residual
142 Steady-State Detection
143 Static Navigation
144 Clock Status
145 Set DGPS Serial Port
20
data neither the alignment nor the byte order
are defined as part of the transport although
SiRF payloads will use the big-endian order.
Checksum
The check sum is transmitted high order
byte first followed byte the low byte. This is
the so-called big- endian order
High Byte
<0x7F
The check sum is 15-bit checksum of the
bytes in the payload data .The following
pseudo code defines the algorithm used. Let
message to be the array of bytes to be sent
by the transport. Let msgLen be the number
of bytes in the message array to be
transmitted .
Index = first
checkSum = 0
while index < msgLen
checkSum = checkSum +message[index]
checkSum = checkSum AND(2
Name
Low Byte
Any value
15
-1)