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RoyalTek GPS Receiver REB-2000/REB-12R REV-2000 Operational Manual
17
following examples:
1. Debug On $PSRF 105,1*3E
2. Debug Off $PSRF 105,1*3F
Table 16 Development Data On/Off Data Format
Name Example Units Description
Message ID $PSRF105 PSRF105 protocol header
Debug 1 0=Off , 1= On
Checksum *3E
<CR><LF> End of message termination
Calculating Checksums for NMEA
Input
The Checksum is the 8-bit exclusive OR of all
the characters after $ and before *. (Not
including $ and *)
SiRF Binary Protocol
The serial communication protocol is designed
to include:
● Reliable transport of messages
● Ease of implementation
● Efficient implementation
● Independence from payload
Protocol Layers Transport Message
Start
Sequence
Payload
Length
Payload
Message
Checksum
End
Sequence
0xA0
1
,
0xA2
Two-bytes
(15-bits)
Up to 2
10-1
(<1023 )
Two-bytes
(15-bits)
0xB0,
0xB3
0xYY denotes a hexadecimal byte value. 0xA0 equals 160.
Transport
The transport layer of the protocol
encapsulates a GPS message in two start
characters and two stop characters. The
values are chosen to be easily identifiable
and such that they are unlikely to occur
frequently in the data. In addition, the
transport layer prefixes the message with a
two-byte (15- bit)message length and a
two-byte(15-bit) choice of a 15-bit values for
length and check sum are designed such
that both message length and check sum
can not alias with either the stop of start
code.
Message Validation
The validation layer is of part of the transport,
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
<0x3F> Any value
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..