Controlling an Attitude director indicator

Hello

I'm a aeronautical engineering student and for my thesis i'm designing a vectoring nozzle.
The movement of the nozzle is controlled with a potentiometric joystick.

These 2 middle pins, go into the analog 0 and 1 inputs of the arduino.

At the same time, an attitude director indicator has to show the corresponding pitch and roll position for the aircraft.
http://www.flightillusion.com/index.php?page=shop.product_details&flypage=ilvm_fly_admirable.tpl&product_id=45&category_id=14&option=com_virtuemart&Itemid=58&vmcchk=1&Itemid=58

The pitch and roll positions are controlled by 2 stepper motors. The attitude indicator has a microcontroller built in and it expects commands like this:

Message layout:
' Byte 1: Flag byte:&h00
' Byte 2: Address: 1-255; (Adress 0 excluded)
' Byte 3: Command: CCCC.1SHL (CCCC=Command 1-15, S= Signbit, H & L are databits)
' The integer is unsigned 16 bits.
' Byte 4: Data Low; &h00-&hFF; bit0 always 1 : XXXX.XXX1 -> XXXX.XXXL
' Byte 5: Data Hight:&h00-&hFF: bit1 always 1 : XXXX.XX1X -> XXXX.XXHX
' Byte 6: LPC Check byte or &hFF ' Commands:
'
' 0= noop
' 1= Initialize
' 2= Set Instrument Address; Value 0-&hff,second byte:&HAA
' 3= Set Instrument speed: If positive: Bank; If negative: Pitch
' 4= Set Bank position (0-4319)
' 5= Set Pitch position (0-1200)
' 6= not used
' 7= Send info about instrument; Reply &h00, Address, Type, Model, Version
' 8= Switch lights: Low byte= DL00.0000; D=display on/off, L=light on/off
' 9= Set Instrument Model &Version, Low Byte=Model, High Byte=Version
' 10= Move bank directly; used for calibration
' 11= Move pitch directly; used for calibration
' 12= Set calibration values for pitch and bank centers
' 13= Clear calibration values for pitch and bank
' 14= Set/Reset testmode: 0=off, 1=on, turn right, 2=on, turnleft

I will only use functions 4 and 5: set pitch and set bank (roll) position.

I don't have a great knowledge of programming, so i'm asking you guys for some help.
How do I write a program for this?

Can you post here a link to the datasheet of this attitude indicator, GSA34?

i haven't found a datasheet online, but I can give you this:

http://www.filehosting.org/file/details/429544/Connector%20pinout.pdf

anyone?