Internal Communications of Celestron
Computerized Telescope Mounts
When it comes to logically troubleshooting problems on a Celestron mount,
it is useful to understand that all of the cabling and interface boards
inside the mount have a single purpose - connecting the hand control to all
of the other individual modules of the system. At a minimum, every current
Celestron computerized telescope has one internal module: the motor control
(a board with two processors, one for each axis). Other possible modules in
the system include GPS, Real Time Clock (RTC), StarSense camera and
Celestron Focus Motor.
Everything in the system is connected together via a shared communication
bus we call the AUX bus. The AUX bus is directly presented outside the mount
via the hand control and AUX ports. The PC Port (for mounts with that port)
is simply the AUX bus with an RS-232 communications buffer to make it
compatible with more external devices, most notably a laptop or desktop
computer. When the SkyPortal WiFi module is plugged into an AUX port, it is
basically presenting the AUX bus via WiFi. For mounts with an internal WiFi
module, that too is basically presenting the AUX bus via WiFi.
Some of the devices on the AUX bus occasionally send out unsolicited packets
of information but generally the hand control initiates all meaningful
communication either sending actionable commands to another module (for
example, movement commands to the MC board or imaging commands to the
StarSense camera) or asking a module for information (for example,
date/time/location info from the GPS module or current ALT/AZM coordinates
from the MC board). The bus is pretty rudimentary in that multiple devices
might send data at the same time, corrupting the messages, so the hand
control is resilient in analyzing received packets and asking for them again
if something is corrupted. Finally, the way the system currently works, all
communication is between the hand control and other modules, the other
modules do not communicate with each other.
If the hand control sends a command to a module and does not receive the
expected reply, it will display a No Response XX error where XX is the
internal device ID of the module. For example, 16 is the device ID of the
azimuth processor in the motor control module while 17 is the ID of the altitude
processor. Read
this
for suggestions on resolving No Response errors.
Note that if you are using SkyPortal/SkySafari or CPWI to replace the hand
control on a system with Celestron WiFi, you can substitute
SkyPortal/SkySafari/CPWI for hand control in most places in the previous
discussion. The same for NexRemote - you can substitute NexRemote for hand
control in the discussion above.
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