Orion SKYQUEST XTG User Manual download pdf (Page 30)

Appendix B: RS-232

Connection

The SkyQuest XTg Mount is designed to receive commands

sent from a computer’s RS-232 COM port (via the computer

interface cable). The hand controller will communicate with the

computer at 9600 bits/sec, no parity, no stop bit. All angles are

communicated with 16 bits and communicated using ASCII

hexadecimal. The chart below shows the ASCII commands

from the PC, and what the hand controller’s response will be.

Additional RS-232 Commands

Sending a Tracking Rate

1. Multiply the desired tracking rate (arcseconds /second)

by 4. For example: if the desired track rate is 120 arcsec-

onds/second (approximately 8 times sidereal rate), then

the TRACKRATE = 480.

2. Separate TRACKRATE into two bytes, such that

(TRACKRATE = TrackRateHighByte*256 +

TrackRateLowByte). For example, if TRACKRATE = 480,

then TrackRateHighByte = 1 and TrackRateLowByte = 224.

3. To send a tracking rate, send the following 8 bytes:

a. Positive Azm tracking: 80, 3, 16, 6,

TrackRateHighByte, TrackRateLowByte, 0, 0

b. Negative Azm tracking: 80, 3, 16, 7,

TrackRateHighByte, TrackRateLowByte, 0, 0

c. Positive Alt tracking: 80, 3, 17, 6, TrackRateHighByte,

TrackRateLowByte, 0, 0

d. Negative Alt tracking: 80, 3, 17, 7, TrackRateHighByte,

TrackRateLowByte, 0, 0

4. The number 35 is returned from the hand controller.

Sending a Slow-GoTo Command

1. Convert the angle position to a 24 bit number. Example:

if the desired position is 220, then POSITION_24BIT =

(220/360)*224 = 10,252,743

2. Separate POSITION_24BIT into three bytes such that

(POSITION_24BIT = PosHighByte * 65536 + PosMedByte

* 256 + PosLowByte). Example: PosHighByte = 156,

PosMedByte = 113, PosLowByte = 199

3. Send the following 8 bytes:

a. Azm Slow Goto: 80, 4, 16, 23, PosHighByte,

PosMedByte, PosLowByte, 0

b. Alt Slow Goto: 80, 4, 17, 23, PosHighByte,

PosMedByte, PosLowByte, 0

4. The number 35 is returned from the hand controller.

Resetting the Position of Azimuth or Altitude

1. Convert the angle position to a 24bit number, same as

Slow-Goto example.

2. Send the following 8 bytes:

a. Azm Set Position: 80, 4, 16, 4, PosHighByte,

PosMedByte, PosLowByte, 0

b. Alt Set Position: 80, 4, 17, 4, PosHighByte,

PosMedByte, PosLowByte, 0

3. The number 35 is returned from the hand controller.

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Orion SKYQUEST XTG User Manual Page 30

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