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3.8
Output
There are six possible NMEA messages, three standard and three proprietary, that can be automatically sent from the
HMR3000 in Continuous Mode by selecting their Update Rates. Additionally, there is a seventh, non-conforming ASCII
display message that can also be sent. The ASCII display message is not expected to commingle with the other six
NMEA messages. It is intended for simpler systems where the HMR3000 is connected to a numerical readout device
instead of a host processor.
The update rate for each message can be set independently to one of the following: 0, 1, 2, 3, 6, 12, 20, 30, 60, 120, 180,
300, 413, 600, 825, or 1200 sentences per minute. If the output channel, due to its programmed baud rate, cannot
accommodate the total number of sentences selected, then the channel will operate at full speed and highest priority will
be given to responses to input, followed by sentences with update rates from lowest to highest. Fairness will be
implemented in the priority scheme so that each sentence ready for output is transmitted at least once before higher
priority sentences are repeated.
3.9
Query for NMEA Sentences
The three NMEA standard sentences (HDG, HDT, and XDR) and three proprietary (HPR, RCD, and CCD) messages
can be queried as follows.
The three standard query messages accepted are:
$TNHCQ,HDG*27<cr><lf>
$TNHCQ,HDT*34<cr><lf>
$TNHCQ,XDR*22<cr><lf>
The three proprietary query messages accepted are:
$PTNT,HPR*78<cr><lf>
$PTNT,RCD*67<cr><lf>
$PTNT,CCD*76<cr><lf>
3.10
Format of NMEA Sentences Output
HDG
Heading, Deviation, & Variation
$HCHDG,x.x,x.x,a,x.x,a*hh<cr><lf>
If either the deviation or variation parameter has not been programmed, the corresponding field will be null (per
NMEA 0183 version 2.1, section 5.2.2.3). Parameters have not been programmed if their absolute values are
greater than 3200 mils or 180.0 degrees. Positive deviation and variation is indicated by a = E; negative values by
a = W. Heading field will be null if it cannot be calculated (see HPR proprietary sentence). NMEA requires that
units for heading measurement be degrees.
Eg.
In Degree Mode
$HCHDG,85.8,0.0,E,0.0,E*77
$HCHDG,271.2,0.0,E,0.0,E*44
$HCHDG,271.1,10.7,E,12.2,W*52
$HCHDG,0.0,10.7,E,12.2,W*57
Mil Mode is not allowed by NMEA standard
HDT
Heading, True
$HCHDT,x.x,T*hh<cr><lf>
The heading field will be null if variation has not been programmed (see HDG and Definitions), or if heading
cannot be calculated. If deviation has not been programmed, it is assumed to be zero, otherwise it is added to
measured heading and variation to express true heading of compass board.
Eg.
In Degree Mode
$HCHDT,86.2,T*15
900240 Rev. B
3/01
page 10
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