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RoyalTek REB-3000 User Manual

Page 25

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RoyalTek RGM-3000/REB-3000
GPS Module Operational Manual)

20

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

Low Byte

<0x7F> Any

value

Even though the protocol has a maximum

length of (215 -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

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

Low Byte

<0x7F Any

value

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

15

-1)

Input Messages for SiRF Binary Protocol

Note – All input messages are sent in BINARY

format

Table 19

SiRF Messages – Input Message List

Hex ASCII

Name

0 x 80

128

Initialize Data Source

0 x 81

129

Switch to NMEA Protocol

0 x 82

130

Set Almanac

0 x 84

132

Software Version

0x 85

133

DGPS Source Control

0x 86

134

Set Main Serial Port

0 x 88

136

Mode Control

0 x 89

137

DOP Mask Control

0 x 8A

138

DGPS Mode

0 x 8B

139

Elevation Mask

0 x 8C

140

Power Mask

0 x 8D

141

Editing Residual

0 x 8E

142

Steady-State Detection

0 x 8F

143

Static Navigation

0 x 90

144

Clock Status

0 x 91

145

Set DGPS Serial Port

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