The Control (CDU) Port is used to initialize, monitor, and control
the receiver. The structure of the control port sentences is based on
the NMEA-0183 Standard for Interfacing Marine Electronics
Navigation Devices (version 1.5). For more details, please refer to
the NMEA-0183 Specification available from the
National Marine Electronics
Association.
Reserved characters are used to indicate the beginning and the end
of records in the data stream, and to delimit data fields within a
sentence. Only printable ASCII characters (Hex 20 through 7F) may be
used in a sentence. Table 2 lists the reserved
characters and defines their usage. Table 1
illustrates the general Magnavox proprietary NMEA sentence format.
Following the start character $, are five characters
which constitute the block label of the sentence. For Magnavox
proprietary sentences, this label is always PMVXG. The
next field after the block label is the sentence type, consisting of
three decimal digits.
The data, delimited by commas, follows the sentence type. Note that
the receiver uses a free-format parsing algorithm, so you need not send
the exact number of characters shown in the examples. You will need to
use the commas to determine how many bytes of data need to be
retrieved.
The notation CK shown in Table 1
symbolically indicates the optional checksum in the examples. The
checksum is computed by exclusive-ORing all of the bytes between the
$ and the * characters. The $ ,
* and the checksum are not included in the checksum
computation.
Checksums are optional for Control Port input sentences, but are
highly recommended to limit the effects of communication errors.
Magnavox receivers always generate checksums for Control Port output
sentences.
ASCII data characters are transmitted in the following format:
Data Bits
8 (msb always 0)
Parity
None
Stop Bits
1
NULL fields are fields which do not contain any data. They would
appear as two commas together in the sentence format, except for the
final field. Some Magnavox proprietary sentences require that the
format contain NULL fields. mandatory NULL fields are identified by an
'*' next to the respective field.
This message enables or disables output of the specified sentence and
defines the output rate. The user sends this message for each sentence
that the receiver is to output.
This message is used to enable/disable the time recovery feature of the
receiver. The time synchronization for the 1PPS output is specified in
addition to a user time bias and an error tolerance for a valid pulse.
This record is accepted in units configured for time recovery. If the
back panel contains a 1PPS outlet, the receiver is a time recovery
unit.
Field
Description
Units
Format
Default
Range
*1
Time Recovery Mode
 
Char
D
D=Dynamic S=Static K=Known Position N=No Time Recovery
2
Time Synchronization
 
Char
G
U=UTC G=GPS
3
Time Mark Mode
 
Char
A
A=Always V=Valid Pulses Only
4
Maximum Time Error
Nsec
Int
100
50-1000
5
User Time Bias
Nsec
Int
0
+/- 99999
6
ASCII Time Message Control
 
Int
0
0=No Output 1=830 to Control Port 2=830 to Equipment Port
Query From a Remote Device / Request to Output a Sentence
Enables the controller to request a one-time transmission of a specific
block label. To output messages at a periodic rate, refer to input
sentence $PMVXG,007.
This sentence gives the receiver position, height, navigation mode and
velocity north/east. This sentence is intended for post analysis
applications.
Field
Description
Units
Format
Range
1
UTC Measurement Time
Seconds into the week
Float
0-604800.00
2
WGS-84 Latitude
DDMM.MMMM
Float
0-89.9999
3
North/South Indicator
 
Char
N, S
4
WGS-84 Longitude
DDDMM.MMMM
Float
0-179.9999
5
East/West Indicator
 
Char
E, W
6
Altitude (MSL)
Meters
Float
 
7
Geoidal Height
Meters
Float
 
8
Velocity East
M/Sec
Float
 
9
Velocity North
M/Sec
Float
 
10
Navigation Mode
 
Int
Navigating
1=Position From a Remote Device
2=2D
3=3D
4=2D differential
5=3D differential Not Navigating
51=Too Few Satellites
52=DOPs too large
53=Position STD too large
54=Velocity STD too large
55=Too many iterations for velocity
56=Too many iterations for position
57=3 Sat Startup failed
This sentence reports the DOP (Dilution Of Precision) values actually
used in the measurement processing corresponding to the satellites
listed. The satellites are listed in receiver channel order. Fields
11-16 are output only on 12-channel receivers.
This sentence is returned (on the Control Port) for every
$PMVXG and $XXGPQ sentence that is
received.
Field
Description
Units
Format
Range
1
Sentence ID
 
Char
 
2
Accept/Reject Status
 
Int
0=Sentence Accepted
1=Bad Checksum
2=Illegal Value
3=Unrecognized ID
4=Wrong # of fields
5=Required Data Field Missing
6=Requested Sentence Unavailable
This sentence is output approximately 1 second preceding the 1PPS
output. It indicates the exact time of the next pulse, whether or not
the time mark will be valid (based on operator-specified error
tolerance), the time to which the pulse is synchronized, the receiver
operating mode, and the time error of the last 1PPS
output. The leap second flag (Field #11) is not output by older
receivers.
Field
Description
Units
Format
Range
1
Time Mark Valid
 
Char
T=Valid F=Not Valid
2
Year
 
Int
1993-
3
Month
 
Int
1-12
4
Day
Nsec
Int
1-31
5
Time
HH:MM:SS
Int
00:00:00-23:59:59
6
Time Synchronization
 
Char
U=UTC G=GPS
7
Operating Mode
 
Char
D=Dynamic S=Static K=Known Position
8
Oscillator Offset - estimate of oscillator frequency error
PPB
Int
 
9
Time Mark Error of last pulse
Nsec
Int
 
10
User Time Bias
Nsec
Int
 
11
Leap Second Flag - indicates that a leap second will occur.
This value is usually zero except during the week
prior to a leap second occurence, when this value
will be set to +/-1. A value of +1 indicates
that GPS time will be 1 second further ahead of
UTC time.