NexStar Info

NexStar Info:
(last updated March 1/2003, 1pm)

Here is some info I've compiled on the NexStar GPS Telescope operation.
Disclaimer: Use this information at your own risk! It is my opinion only.

Feel free to mail me at: andre@paquettefamily.ca for any comments, corrections, or suggestions.

NexStar AUX Command Set
Hand Controller
Motor Controller
GPS Module
Serial Problem with HC
Autoguiding with Joy(stick)
PC Control Cables

NexStar AUX Command Set:

This document describes the packet format and protocols used within the NexStar GPS telescopes. I've called these commands the AUX command set. These are not the same commands currently used to control the telescope from the HC serial port. The AUX command set operates at a low level and gives access to all the fundamental operations within the telescope. For example, the AUX commands allow you to:

use the PC port to control the telescope
access information like GPS time/site via HC serial port or PC port
control all aspects of MC operation, like leveling, movement and positioning, backlash settings, etc.
perform firmware upgrades of the MC
design other devices that plug into the AUX port that can be accessed from the HC serial or PC port

This document is highly technical in nature and is written mainly for programmers wanting to develop or enhance computer interfaces to the telescope. It is hoped that this information allows people to do new and exciting things with their NexStar telescopes and that interest in these telescopes will increase due to the knowledge of their very flexible and powerful design.

Here is version 1.0 of the AUX command set document: NexStar_AUX_Commands_10.pdf

Many thanks go to Ray St. Denis, Stacey Sheldon, Mike Zeidler, and Carlene Paquette for help with this document.

Ray has put together a useful application as a demo of the AUX command set and for experimentation with the PC port. It displays the packets received over the PC port so that communications between the HC and other modules can be monitored. It also displays firmware versions and allows you to slew the telescope in various directions.
Here is version 1.2 of Ray's NexTest application: NexTest1_2.exe.

Ray has also made an excellent configuration utility using the AUX command set, called NexConfig. This app uses the hand controller serial port, so you don't need to make a PC-port cable for this. You can find it at:
http://www.StDenisSoftware.com/Download/NexConfigInstall.exe

I've put together a couple of small (WIN32) utilities to help diagnose various communications problems with HC/MC:

getver:

Polls the versions of the MC ALT/AZM, GPS, and M/IB boards. Can be used from either the HC serial or PC port interface.
Usage: getver <comport> <mode> <count> [debug], where:

<comport> is the com # (ie., 1 for com1)
<mode> is 0 for PC port and 1 for HC serial
<count> is the number of times to poll each device
[debug] is an optional debug level. Use a value of 2 to see packet contents.

monitor:

Monitors traffic and displays raw bytes on the PC port interface.
Usage: monitor <comport>, where:

<comport> is the com # (ie., 1 for com1)

Hand Controller:

The NexStar GPS hand controller employs a PIC17C756A processor.

The HC firmware can be found in two socketed chips. These chips are Atmel AT49F040 512K flash devices .

With the HC display on the top, the leftmost flash device is the "even" part -- the chips have 2 dots on the top.
The rightmost device is the "odd" part and has 1 dot on the top.

Firmware can be extracted from the flash devices and units upgraded via a programmer.
Note that the sockets are quite fragile and it takes a fair bit of force to remove the chip, so be sure to use proper chip removers if you intend to play -- and be careful.
Finally, here is the manual for HC 1.6 features.

Debug mode:
There is a hidden mode in the hand controller that gives you access to some low-level information. To enter this mode, hit 6, then 7 from the "NexStar GPS" level.
Here's what this mode gives you:

Action/Version	1.6	2.2
Mode entered	"up time" displayed	blank screen
1 Button	N/A	read/write seep
3 Button	read/write seep	read/write seep
7 Button	get compass heading	get compass heading
8 Button	get detailed GPS info	N/A
0 Button	displays HC version, allows retrieval of version from other devices	N/A

For the detailed GPS info, the displayed format is:
"A B H:M:S"
"CD E F G"
Where:
A is the number of tracked satellites,
B is the MSB of the RCVR Status
H:M:S is the time in GMT
C is the month
D is the day
E, F, and G are the raw values for the latitude.

Motor Controller:

The NexStar GPS motor controller employs two PIC16F876 devices, one for each axis. A schematic for the MC board can be found here.

Buying a PIC programmer:
Programmers are not expensive and can be found at:
http://www.phanderson.com/

PIC development software:
The MPLAB software for the PIC programmer can be downloaded for free from Microchip at:
http://www.microchip.com/1010/pline/tools/picmicro/devenv/mplabi/mplab5x/index.htm

Intel Hex format:
Information on the Intel Hex format can be found at:
http://www.cs.net/lucid/intel.htm

Upgrading the MC firmware:
It is possible to upgrade the MC board by:
a) getting a new board with new firmware from Celestron or another authorized dealer
b) programming new firmware via a PIC programmer
c) downloading new firmware using the AUX command set

GPS Module:

The NexStar GPS module consists of two boards: Celestron's controller board and Motorola's M12 GPS module.

Celestron's controller board uses the PIC16F876 processor, which is also used on the motor controller board. Additional resources for this device can be found here. Schematics are available for the GPS board here but they omit the fact that the programming pins are brought out to an (unpopulated) header position as with the MC board.

The Motorola GPS board is very well documented here. The chapter 5 document on that page lists all of the commands supported by that board.

Note that the GPS antenna is located at the top of the fork arm with the handle, so it is important not to block that area when getting a GPS link.

Serial problem with HC:

Not all PC serial ports are made equal. When not in use, most serial ports idle with a stop bit. However, some serial ports send a continuous start bit (break signal) when not in use. If the HC serial port receives a continuous start bit, it gets confused or bogged down and has difficulties sending characters the next time you connect. For instance, if you try connecting to the HC with "TheSky" you'll get errors 9/10 times.
Often, BIOS upgrades are available that will change the serial port behaviour and work around the problem. Also, you could get a serial-to-USB device and hope that it idles with stop bits.
Either way, this is a bug with the serial handling on the HC and hopefully Celestron will correct it on the next spin.

Autoguiding with Joy(stick):

It it is really easy to make a cable that allows the autoguider port to interface with the old-style Commodore/Atari joysticks. These old joysticks will fit into a male DB9 connector and are great for doing manual guiding. Wico command/control meets NexStar GPS...

AG pin 1 -> N/C
AG pin 2 -> DB9 pin 8 (GND)
AG pin 3 -> DB9 pin 4 (+RA)
AG pin 4 -> DB9 pin 1 (+DEC)
AG pin 5 -> DB9 pin 2 (-DEC)
AG pin 6 -> DB9 pin 3 (-RA)

PC Control Cables:

Cables for sale
Parts used
9-pin serial pinout
HC serial pinout
PC port pinout

Cables for sale:

I'm selling cables (at just over cost) for interfacing your computer to the NexStar telescopes.
There are two kinds of cables: one to connect to the hand controller, and one to connect to the PC port. The table below lists the prices. Shipping is extra.

Part	Canadian $	US $
Complete HC Serial Cable	$7.78 + $0.12/foot	$5.12 + $0.08/foot
Complete PC Port Cable	$7.98 + $0.18/foot	$5.24 + $0.12/foot
DB9F to RJ45 Adapter Only	$6.87	$4.52
HC Serial Cable Only (no DB9 end)	$0.91 + $0.12/foot	$0.60 + $0.08/foot
PC Port Cable Only (no DB9 end)	$1.11 + $0.18/foot	$0.73 + $0.12/foot

Cables are made from 4 or 6 conductor flat cable with an RJ45 connector at one end and either an RJ45 or RJ11 handset plug at the other end. The RJ45 connector plugs into an adapter that converts the RJ45 to a 9-pin female end for use with a computer.

If you wanted both a PC port and a HC serial cable but weren't going to use both at the same time, you could buy one "DB9F to RJ45 Adapter" and then the "Cable Only" parts for each type of cable.

If you're interested in purchasing a cable, send me an email with the type, length and number of cables you would like and the address to use for shipping. I'll then send you an email when the cable is ready and the expected cost including shipping. You can then send me a cheque and I'll send you the goods.

Here are the parts used to make the cables:

DB9F to RJ45 modular connector
RJ45 plug
RJ11 handset plug
"Silver Satin" 6-conductor cable
"Silver Satin" 4-conductor cable

Here is the pinout for the DB9F connector:

Pin 2 -> data to computer from telescope
Pin 3 -> data from computer to telescope
Pin 5 -> ground
Pin 7 -> RTS
Pin 8 -> CTS

Here is the pinout for the HC Serial interface:

Pin 1 -> data to computer from telescope
Pin 2 -> ground
Pin 4 -> data from computer to telescope

Additional information on how to make a HC serial cable can be found on Mike Swanson's site.
Important: Pin1 is the pin on the lower right side of the diagram on Mike's page.

Here is the pinout for the PC Port interface:

Pin 1 -> ground
Pin 2 -> data from computer to telescope
Pin 3 -> ground
Pin 4 -> data to computer from telescope
Pin 5 -> RTS
Pin 6 -> ground
Pin 7 -> CTS
Pin 8 -> ground

Additional information on how to make a PC port cable can be found on Mike Swanson's site.
Important: Pin1 is the pin on the lower right side of the diagram on Mike's page.