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New NexStar GPS Commands

Mike Swanson
swanson.michael@usa.net
http://www.angelfire.com/ns/nexstar


Tracking Rate Commands


1. Multiply the desired tracking rate (arcseconds per second) by 4
Example: if the desired trackrate is 150 arcseconds/second, then
TRACKRATE = 600 (sidereal rate is basically 15 arcsecond/second, so the
trackrate would be 60)

2. Break up TRACKRATE into two bytes, such that TRACKRATE =
TrackRateHigh*256 + TrackRateLow
Example: TrackRateHigh = 2
TrackRateLow = 88

3. For positive Azm tracking (move to the right), send the following 8
bytes to the RS232 connection on the bottom of handcontrol (note that the
commas are not sent):
80, 3, 16, 6, TrackRateHigh, TrackRateLow, 0, 0

4. For negative Azm tracking (move to the left), send the following 8
bytes to the RS232 connection on the bottom of handcontrol (note that the
commas are not sent):
80, 3, 16, 7, TrackRateHigh, TrackRateLow, 0, 0

5. For positive Alt tracking (move up), send the following 8 bytes to the
RS232 connection on the bottom of handcontrol (note that the commas are not
sent):
80, 3, 17, 6, TrackRateHigh, TrackRateLow, 0, 0

6. For negative Alt tracking (move down), send the following 8 bytes to
the RS232 connection on the bottom of handcontrol (note that the commas are
not sent):
80, 3, 17, 7, TrackRateHigh, TrackRateLow, 0, 0

7. In all cases the number 35 is returned from the handcontrol to show
communication is ok.

8. The tracking rate returns to the hand control default (usually sidereal)
after any of the following:
after approximately 20 seconds with no action from the PC or the user
after pressing any of the arrow buttons on the hand control

To prevent this automatic return to default tracking, you must set the
tracking mode to Off prior to issuing a new tracking rate command.



Tracking Mode Command


The command to turn off tracking is:

"T", 0 - this is a binary 0, not a text 0

Then to return to sidereal rate, use one of the following:

"T", 1 starts Alt/Az tracking
"T", 2 starts EQ North tracking
"T", 3 starts EQ South tracking

Again, the numbers are binary values, not text 1, 2, or 3.

The sequence would be Tracking Off command, Tracking Rate command(s), ...
wait as long as you want... then Tracking On (1, 2, or 3 as appropriate)
command.

Unfortunately there is no command to determine what tracking mode was
initially in effect, so the user interface of a program must ask the user
to provide the correct tracking mode.


In the simplest sense, the tracking command simply emulates the buttons on
the hand control. It can be used to provide a way to manual slew via the
RS-232 port. It can be used to provide a set of direction buttons in a PC-
based program or it could be used to program a sophisticated autoguider
(although it should be noted that unless you are attempting to interpret
images from an inexpensive PC camera and then in turn autoguide, there are
better, self contained products already on the market). It may also be
possible to allow a PC to control tracking of a satellite.


32 bit Commands

GoTo RA-Dec:
PC sends: r34AB0500,12CE0500 <== don't forget the comma!
Where 'r' is the command, '34AB0500' is the RA coordinate in hex format and
'12CE0500' is the Dec coordinate in hex format. Refer to the spreadsheet
'EncoderCalculations.xls' to learn how to calculate these coordinates.
The scope will reply with '#'. Note that the last byte (last two
characters in each coordinate) will always be 00 as the encoder resolution
does not exceed the use of the first 3 bytes.

Get RA-Dec:
PC sends: e
The scope replies: 34AB0500,12CE0500#
Where '34AB0500' is the RA coordinate in hex format and '12CE0500' is the
Dec coordinate in hex format.


Get Hand Control Version (works on new GT hand control as well):
PC sends: V
The scope replies with the version number (as an ASCII code), a 0 and
#