Celestron NexStar 8i manual Appendix D RS-232 Connection, Communication Protocol

Appendix D - RS-232 Connection

You can control your NexStar telescope with a computer via the RS-232 port on the computerized hand control and using an optional RS-232 cable (#93920). Once connected, the NexStar can be controlled using popular astronomy software programs.

Communication Protocol:

NexStar-i communicates at 9600 bits/sec, No parity and a stop bit. All angles are communicated with 16 bit angle and communicated using ASCII hexadecimal.

Description

PC Command ASCII

Hand Control Response

Notes

Echo	Kx	X#	Useful to check communication
Goto Azm-Alt	B12AB, 4000	#	10 characters sent. B=Command,
			12AB=Azm, comma, 4000=Alt. If
			command conflicts with slew limits,
			there will be no action.
Goto Ra-Dec	R34AB, 12CE	#	Scope must be aligned. If
			command conflicts with slew limits,
			there will be no action.
Get Azm-Alt	Z	12AB, 4000#	10 characters returned,
			12AB=Azm, comma, 4000=Alt, #
Get RA-Dec	E	34AB, 12CE#	Scope must be aligned
Cancel Goto	M	#
Is Goto in Progress	L	0# or 1#	0=No, 1=Yes; "0" is ASCII
			character zero
Is Alignment Complete	J	0# or 1#	0=No, 1=Yes
Commands below available
on version 1.6 or later
HC version	V	1 6 #	Version 1.6
Stop/Start Tracking	Tx	#	Alt-Az tracking requires alignment
	x = 0 (Tracking off)
	x = 1 (Alt-Az on)
	x = 2 (EQ-N)
	x = 3 (EQ-S)
32-bit goto RA-Dec	r34AB0500,12CE0500	#
32-bit get RA-Dec	e	34AB0500,12CE0500#	The last two characters will always
			be zero.
32-bit goto Azm-Alt	b34AB0500,12CE0500	#
32-bit get Azm-Alt	z	34AB0500,12CE0500#	The last two characters will always
			be zero.

The cable required to interface to the telescope has an RS-232 male plug at one end and a 4-4 telephone jack at the other end. The wiring is as follows:

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