your position is our focus
Th
following
table
g
e
ives
information
about
the
various
values:
Nu b
m er Formats
Short
Comment
Min/Max
Resolution
Type Size
(Bytes)
U1
0...255
1
Unsigned
Char
1
I1
plement
-128...127
1
Signed
Char
1
2's
com
U2
0...65535
1
Unsigned
Short
2
I2
2's
complement
-32768...32767
1
Signed
Short
2
U4
0…4'294'967'295
1
Unsigned
Long
4
I4
plement
-2'147'483'648...
2'147'483'647
1
Signed
Long
4
2's
com
R4
-1*2^+127…2^+127
~Value
*
2^-24
IEEE
754
Single
Precision
4
R8
8
-1*2^+1023...2^+1023
~Value
*
2^-53
IEEE
754
Double
Precision
CH
ASCII
/
ISO
8859.1
Encoding
1
Table 25: Internal Field Number Formats
UBX h
The
ting
and
including
the
CLASS
field,
up
until,
but
excluding,
the
Che
C ecksum
checksum
is
calculated
over
the
packet,
star
cksum
Field:
Figure 71: UBX Checksum range
The
checksum
algorithm
used
is
the
8-Bit
Fletcher
Algorithm,
which
is
being
used
in
the
TCP
standard
(RFC
1145).
This
algorithm
works
as
follows:
Buffer[N]
contains
the
data
over
which
the
checksum
is
to
be
calculated.
The
two
CK_
values
are
8-Bit
Unsigned
Integers,
only!
If
you
implement
it
with
larger-sized
integer
values,
make
sure
to
mask
both
CK_A
and
CK_B
with
0xFF
after
both
operations
in
the
loop.
CK_ A = 0, CK_B = 0;
For(i=0; i<N; i++)
{
CK_A = CK_A + Buffer[i];
CK_B = CK_B + CK_A;
}
After
the
loop,
we
end
up
having
two
UINT8
values,
which
are
transmitted
at
the
end
of
the
packet.
GPS
Modules
-
System
Integration
Manual
(SIM)
(incl.
Reference
Design)
Receiver
Description
GPS.G4-MS4-05007-A1
Page 84
