It is recommended that you use the "hc" driver if you are planning on using the
telescope with a computer attached, and will be at the telescope when you turn
on the driver power.  If not, read on.

Celestron mountings typically have three electronic interfaces labeled:

PC  -- A true RS232 port that connects directly to the motor controllers.
HC  -- A RS232 connector on the hand controller.
AUX -- A TTL serial connector that is otherwise identical to the PC connection.

There are two different control languages -- one uses the power of the hand
control computer and celestial coordinates (hc command set), the other is a
hardware language that is unaware of the sky (aux command set). The aux command
set may be accessed through the HC, PC or AUX ports.  The hc command set may be
accessed only through the HC port. 

It is simpler than it sounds.  

The PC port on our Celestron mounts is very sensitive to electrical 
interference and is unreliable.  In short, the advice is not to use it. 

The AUX port is a TTL interface.  Without additional components it cannot be
used as an interface for the mount.

Therefore, always connect your computer to the telescope through the serial port
on the hand control, the "HC" port.  

For the most reliable operation --

Use the HC driver. Initialize the pointing as if you were going 
to observe "hands-on."  Run the telescope from your computer.

If you need to start the telescope remotely and run without an operator from
power-on to power-off --

Use the AUX driver. For a German Equatorial, have the OTA over the pier
pointing at the pole when you apply power to the mount. Do not initialize the
hand control, but simply turn on the power and then run from your comptuer.

The subdirectories have files for the three different modes of operation of a
Celestron telescope with NexStar motor controllers. Use the "setup_nexstar_hc"
and "setup_nexstar_aux" scripts when compiling.  You will only need to edit in
the aux directory if there are gearing ratio changes for your mount that have to
be set.


hc 
==

The serial port of the computer is connected to the hand control (HC) as
described in the NexStar telescope manuals for interfacing the telescope to a
computer.  The telescope must go through the manual startup process and 
requires hands-on intervention to operate in the usual way after power is 
turned on.   Once started, however, it will run remotely on this interface, 
and RA and Dec  positioning will be available manually through the hand paddle.


aux 
===  

The serial port of the computer is connected to the hand control (HC) as
described in the NexStar telescope manuals for interfacing the telescope to a
computer. The telescope does not go through a manual startup process, and  its
position is set by direct commands to the motor drives.  The internal software
in the hand paddle for positioning is bypassed in this mode.  Use this if you
want to turn on the telescope remotely without an operator present and rarely 
use the hand control at the telescope.

In its present state of development, the aux driver header must be modified by
the end user to match the their own telescope gearing.  With the parameters
given here, the driver works for our large German equatorials which were
prototypes for the current (2010) CGE "Pro".  

We expect to provide appropriate parameters for the NexStar fork mounts and the
CGE Pro but you may have to set these in the header files before compiling.


pc 
==

The serial port of the computer is connected to a PC port on the telescope. 
This interface provides a direct connection to the two motor control boards and
does not use the features of the hand controller.  It is primitive, and
lacks the user safeguards of the hand control.  

This inteface does not work on most mounts due to electronic issues with the 
RS232 circuitry. If the mounting does not respond to the hand control when the
computer is connected to the PC port, that may the case with your mounting. The
simplest solution is to use the aux system described above and the HC  wiriing
interface. There are some third-party buffers for the PC port that could fix 
this but we do not have access to one.

At this time the software for this interface is incomplete because of a hardware
issue with the mountings on which we test xmtel. We have left the undeveloped
code here because it has the communications components that would be needed for
a successful version. The code is not updated for the current version of xmtel
and would require work to get it functional.