connect the outputs of both ports (TxD to TxD) and inputs (RxD to RxD) to each other. 

The null modem adapter will cross TxD to RxD. 

Alternatively, a cable can be made with an RJ22 plug as described in section 6.1, but with 

a male DB9 connector and the RxD and TxD wires swapped. 

Once you have connected your GPS receiver to Gemini, you should configure your GPS 

to output either Garmin Textout protocol, or NMEA 0183 protocol.  Gemini requires only 

the   Recommended Minimum   (RMC) NMEA 0183 sentence to be sent, which is 

supported by all GPS receivers.  In addition to the NMEA standard baud rate of 4800, 

Gemini will also try 9600 baud when it checks for GPS data. 

6.4  Using Planetarium Programs 

You can use many popular planetarium programs to control your Gemini.  Most will 

allow you to select any object and command Gemini to go to that object.  Many will also 

show where on the sky Gemini is pointing. 

6.4.1  Telescope Driver  

 Some popular planetarium programs come with a dedicated Gemini driver; if not, they 

will have an LX200 driver that should work flawlessly.   Examples of Windows PC 

planetarium programs that are successfully being used with Gemini are TheSky, Guide, 

SkyMap, and Starry Night. In addition, Voyager and Starry Night can be used on 

Macintosh, XEphem under Linux, and TheSky PE on PDAs.   

6.4.2  Communication Port Access 

One disadvantage of a serial port is that it cannot be shared between programs. If you 

plan to use a planetarium program such as TheSky and the Gemini Control Program GCP 

together, you will have to toggle the serial link off in one program to activate it in the 

other. If the program provides this capability, there will be no need to stop the programs 

and restart.  

6.4.3  Coordinate Epoch 

Gemini expects the coordinates sent from a PC to be precessed to either the standard 

epoch J2000.0 or to the equinox of the date. You can select the appropriate epoch using 

the   Setup

Coordinate Epoch   menu item. If J2000.0 coordinates are selected, Gemini 

precesses the coordinates once they are received. If   Equinox of the Date   is selected, no 

precession calculation is done and the coordinates are expected to be correct for the 

current date. 

NOTE:  These settings only apply to data sent 

from

 the PC 

to

 Gemini.  Coordinates sent 

from Gemini to the PC always refer to the Equinox of the current date.  This avoids 

confusion for the software that is controlling the Gemini system. 

NOTE:  A program can send J2000.0 coordinates (using :Sr, :Sd commands) followed by 

a precess command :Sp#. Gemini checks its settings and if   Equinox of the date   is 

active, the precession calculation will be done. If   J2000.0   is active, the coordinates 

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