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HMR3000 User's Guide
The HMR3000 supports both standard NMEA 0183 and proprietary messages. Unsolicited NMEA messages are sent by
the HMR3000 in Continuous Mode at the rates programmed in EEPROM. HMR3000 also responds to all input messages
from the host. An HMR3000 response to a command input may be delayed due to transmission of an unsolicited output.
The host processor must wait for HMR3000 to respond to the last command input before sending another command
message.
All communication from and to HMR3000 contain a two-character Checksum Field at the end of the data fields, and are
denoted in the following sentences by 'hh'. The checksum assures the accuracy of the message transmitted. This
checksum is calculated per NMEA 0183 Standard, and is outlined in section 3.11.
3.7 HMR3000 Input Data
There are two kinds of serial data input to the HMR3000; either a request for output sentence, or a setting of a
configuration parameter.
HMR3000 sends a response to all valid inputs with a correct checksum value.
1. Response to a Request for output sentence is the appropriate sentence.
2. Response to parameter input will be #!0000*21 to indicate the command and the parameter was accepted.
3.8 HMR3000 Output Data
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>
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