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Celestron 21020 Communication Protocol Manual

Nexstar hand control
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NexStar Communication Protocol
This document describes the serial commands supported by the Celestron NexStar hand control. This information
applies to the NexStar GPS, NexStar GPS-SA, NexStar iSeries, NexStar SE Series, NexStar GT, CPC, SLT, Advanced-
GT, and CGE mounts.
Communication to the hand control is 9600 bits/sec, no parity and one stop bit via the RS-232 port on the base of the
hand control.
Note: the GT hand control prior to version 104.0 should be treated as version 1.2 in the tables below. Version 104.0
should be treated as version 4.03.
Get Position Commands
The following commands retrieve the position of the telescope in either RA/DEC or AZM-ALT coordinates.
The position is returned as a hexadecimal value that represents the fraction of a revolution around the axis. Two
examples are given below:
If the Get RA/DEC command returns 34AB,12CE then the DEC value is 12CE in hexadecimal. As a percentage
of a revolution, this is 4814/65536 = 0.07346. To calculate degrees, simply multiply by 360, giving a value of
26.4441 degrees.
If the precise GET AZM-ALT command returns 12AB0500,40000500 then the AZM value is 12AB0500 in
hexadecimal. As a percentage of a revolution, this is 313197824/4294967296 = 0.0729 or 26.252 degrees.
The standard commands offer a precision of 1/65536 * 360 * 60 * 60 = about 19.8 arcseconds per unit while the precise
commands offer a precision of 1/16777216 * 360 * 60 * 60 = about 0.08 arcseconds per unit (only the upper 24 bits are
used).
Note: if the telescope has not been aligned, the RA/DEC values will not be meaningful and the AZM-ALT values will
be relative to where the telescope was powered on. After alignment, RA/DEC values will reflect the actual sky,
azimuth will be indexed to North equals 0 and altitude will be indexed with 0 equal to the orientation where the optical
tube is perpendicular to the azimuth axis.
Command Function
Get RA/DEC
Get precise RA/DEC
Get AZM-ALT
Get precise AZM-ALT
GOTO Commands
The following commands direct the telescope to GOTO a specified RA/DEC or AZM-ALT position. As with the Get
Position commands, the values are in hexadecimal and represent the fraction of a rotation around the axis.
Note: GOTO RA/DEC commands will not work unless the telescope is aligned.
Command Function
GOTO RA/DEC
GOTO precise RA/DEC
GOTO AZM-ALT
PC Command
Hand Control
Response
"E"
"34AB,12CE#"
"e"
"34AB0500,12CE0500#"
"Z"
"12AB,4000#"
"z"
"12AB0500,40000500#"
PC Command
"R34AB,12CE"
"r34AB0500,12CE0500"
"B12AB,4000"
Applies to
Versions
1.2+
1.6+
1.2+
2.2+
Hand
Applies to
Control
Versions
Response
"#"
1.2+
"#"
1.6+
"#"
1.2+

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  Summary of Contents for Celestron 21020

  • Page 1 NexStar Communication Protocol This document describes the serial commands supported by the Celestron NexStar hand control. This information applies to the NexStar GPS, NexStar GPS-SA, NexStar iSeries, NexStar SE Series, NexStar GT, CPC, SLT, Advanced- GT, and CGE mounts. Communication to the hand control is 9600 bits/sec, no parity and one stop bit via the RS-232 port on the base of the hand control.
  • Page 2: Tracking Commands

    Slewing Commands The following commands allow you to slew (move) the telescope at fixed or variable rates. For variable rates, multiply the desired rate by 4 and then separate it into a high and low byte. For example if the...
  • Page 3 Command Function Variable rate Azm (or RA) slew in positive direction Variable rate Azm (or RA) slew in negative direction Variable rate Alt (or Dec) slew in positive direction Variable rate Alt (or Dec) slew in negative direction Fixed rate Azm (or RA) slew in positive direction Fixed rate Azm (or RA)
  • Page 4 slew in positive direction Fixed rate ALT (or DEC) slew in negative direction Time/Location Commands (Hand Control) The following commands set the time and location in the hand control. The format of the location commands is: ABCDEFGH, where: A is the number of degrees of latitude. B is the number of minutes of latitude.
  • Page 5: Gps Commands

    Get Location Set Location Get Time Set Time GPS Commands The following table shows various commands that can be sent to a GPS unit. Note: all units of time are in UT. Command Function Is GPS Linked? X > 0 if linked, 0 if not linked Get Latitude ((x*65536)+(y*256)+z)/(2...
  • Page 6: Rtc Commands

    ^24) is a fraction of a rotation. To convert to degrees, multiply by 360. Get Longitude ((x*65536)+(y*256)+z)/(2 ^24) is a fraction of a rotation. To convert to degrees, multiply by 360. Get Date x is month (1-12) y is day (1-31) Get Year (x * 256) + y = year Get Time...
  • Page 7: Miscellaneous Commands

    Get Year (x * 256) + y = year Get Time x is the hours y is the minutes z is the seconds Set Date x is month (1-12) y is day (1-31) Set Year (x * 256) + y = year Set Time x is the hours y is the minutes...
  • Page 8: Developer Notes

    Pass-through Commands with No Response Commands that start with ‘P’ are special pass-through commands that communicate with a specific telescope device. For instance, the Slew commands talk directly to the motor control. If a ‘P’ command is sent but no response is returned (because the device is not there or the command is unknown or there was a communication problem) then one extra data byte is returned before the ‘#’...