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This module connects the Rocky Mountain µEncoder (input) and the Honeywell Compass (input).


  • USART0, RS232, RX/TX, uE
  • USART1, RS232, RX/TX, HC
  • no power


RX0: uE - Rocky Mountain µEncoder Standard Format

The standard Rocky Mountain µEncoder serial port output format (SEr/OUtPt/Std menu selection) contains all of the µEncoder functions including those not shown on the display. The string of data is output once per second with a baud rate set using the SEr/BAUd/xxxxx programming menus. Voltage levels meet the RS232 standard, but with maximum voltage levels that will work with RS422 and RS485 equipment. Protocol is 1 start bit, 8 data bits and 1 stop bit. Each byte of data is an ASCII character (with exceptions noted).

Each field is output with the most significant digit first which may contain leading blanks or a minus sign.

The sign byte is not in a fixed position, ie -1234 and (blank)-567 are two valid outputs for the same function. Positive numerical fields are assumed unless a minus is present. If a field is out of limits for the µEncoder the field will be filled with Es (for error). If the temperature probe of the µEncoder is inoperative or disconnected, temperature dependent functions such as true airspeed, density altitude etc. will have their fields filled with Es.

The standard output format is:

Byte# Ck Name Description
01 ID#1 hex ident byte - always FF hex (FF81h can't be duplicated in following string)
02 ID#2 hex ident byte - always 81 hex
03  * Mode output format code - always BINARY 1 for standard format
04 - 08  * IALT indicated altitude (1)
09 - 13  * PALT pressure altitude (1)
14 - 18  * DALT density altitude (1)
19 - 23  * TALT true altitude (see WARNING in ALt/GndSn menu) (1)
24 - 28  * AlertALT alert altitude currently set (use indicator flags to see if alert is active)
29 - 31  * IAS indicated airspeed in knots or MPH
32 - 34  * TAS true airspeed in knots or MPH
35 - 38  * Mach indicated airspeed in mach (assume decimal, (blank)453 = .453 mach)
39 - 42  * VSI VSI in 10's of FPM - multiply output times 10 (1)
43 - 45  * OAT indicated outside air temperature (EC only) (1)
46 - 48  * TAT true air temperature (static temperature) (EC only) (1)
49 - 52  * InHg altimeter setting in inches of mercury OR millibars (decimal assumed between 2nd and 3rd digits for inches of mercury)
53 - 56  * Inds BINARY bytes containing bit indicator flags (gear, flap etc.) - bit=1 means indicator is being shown on display - see below for breakdown
57 - 60  * Hdg compass heading from external heading sensor (assume decimal ddd.d)
61  CkByte BINARY checkbyte for all bytes in list marked with "*" - CkByte added to string byte total (mod 256) will equal zero if a valid string received

(1) - Can contain minus sign.

Indicator Bit# Byte 1 Byte 2 Byte 3 Byte 4
0 FT/ALT CONV FPM ignore
1 EF TAS TAT ignore
2 HOLD KT EC ignore
3 Vno IAS LGT ignore
4 Vne UPATI HDG ignore
5 APP DOWNATI InHg ignore
6 FLAP M Mb ignore
7 GEAR mach decimal point baro setting decimal ignore

RX1: HC - Honeywell NMEA

(source: the Honeywell manual 900240 rev. B, 3.10 Format of NMEA Sentences Output)

HDT Heading, True


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


Mil Mode not allowed by NMEA standard

HDG Heading, Deviation, & Variation


If either the deviation or variation parameter has not been programmed, the corresponding field will be null (per NMEA 0183 version 2.1, section 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


Mil Mode is not allowed by NMEA standard

XDR Transducer Measurements


Each of the six possible measurements - pitch; roll; and magnetic x, y, z, and totalócan be individually included in or excluded from the message (see ìXDR has Öî parameters). See NMEA 0183 for a detailed description of the Type-Data-Units-ID field encoding. The ìDataî field of an included measurement will be null if its contents cannot be determined due to saturated measurements. Only units of degrees are allowed by NMEA for pitch and roll measurements. Magnetic measurements are transmitted in engineering units (milli Gauss) determined by a tunable conversion factor. MAGX aligns with the compass board north-south axis, and MAGZ is perpendicular to the plane of the compass board. MAGT is the total magnetic field strength determined by calculating the square root of the sum of the squares of MAGX, MAGY, and MAGZ.

Eg. In Degree Mode


In Mil Mode


HPR Heading, Pitch, & Roll


This sentence combines HMR3000ís three significant measurements with useful status information. Data fields represent, in order: heading, magnetic field status, pitch, pitch status, roll, and roll status. Heading, pitch, and roll measurements are presented in degrees or mils depending on the setting in EEPROM. The heading measurement is corrected for deviation and variation when these factors are programmed in the EEPROM.

Eg. In Degree Mode


In Mil Mode


Status fields can contain one of six letter indicators:

  • L = low alarm,
  • M = low warning,
  • N = normal,
  • O = high warning, or
  • P = high alarm.
  • C = Tuning analog circuit

If any of the three status fields indicates alarm, then the heading field will be null as well as the corresponding measurement field. Thresholds for alarm and warning levels can be changed in the EEPROM.

RCD Raw Compass Data


This sentence provides raw tilt and magnetic measurements for diagnostic use. Contents of each field represent A/D readings for, in order: TiltAp, TiltAm, TiltBp, TiltBm, MagA, MagB, MagC, MagAsr, MagBsr, MagCsr. All values represent the actual A/D readings from the most recent conversions, except that tilt readings are adjusted if low gain was used for the conversion. Mag_sr values represent the sum of the most recent calibration Set and Reset pulse measurements for each sensor. There are never any null fields in this sentence.

Eg. In Degree Mode


In Mil Mode


CCD Conditioned Compass Data


This sentence provides conditioned tilt and magnetic measurements for diagnostic use. The fields are, in order:

  • TiltX 32768 times tangent of angle between compass board north-south axis and level plane. This value is the difference between the raw tilt measurements normalized, linearized, and filtered according to parameter settings. The pitch measurement is determined by taking the arctan of TiltX/32768.
  • TiltY same as TiltX but for the compass board east-west axis (roll).
  • MagX normalized and filtered magnetic field strength along the north-south axis of the compass board. This value has been adjusted for any hard-iron offset determined during calibration (or tuned manually).
  • MagY same as MagX but along the compass board east-west axis.
  • MagZ same as MagX and MagY, but along the axis perpendicular to the plane of the board. This value has been adjusted both for gain variation with the X-Y sensor pair and for hard-iron.
  • MagT Total magnetic field strength

Heading calculated heading based on the magnetometer and inclinometer data in this sentence. Presented in degrees or mils depending on the setting in EEPROM. This field will be null if the heading cannot be calculated.

Eg. In Degree Mode


In Mil Mode