In normal use, the Rotator unit handles all communications and will forward commands and responses to and from the shutter unit. For diagnostic purposes, it is also possible to issue shutter commands directly to the shutter unit by connecting a USB cable. The shutter will not forward commands to the rotator.

Commands have the form:

@ Verb target , Parameter <CR><LF>

The parts of this command syntax are:

• @ is a literal character that marks the start of a new command and clears the receive buffer.
• Verb is the command verb, which normally consists of two characters. Single character verbs are also possible but in this case the entire command is a single character.
• Device is the target device for the command, generally R (rotator) or S (shutter).
• , is a literal character that separates the device ID from the parameter. The comma is required if a parameter is present and should be absent if there is no parameter.
• Parameter is usually a signed or unsigned decimal integer and is the data payload for commands that need data. Refer to the notes for each command for specific requirements.
• <CR><LF> is the command terminator and submits the command to the command dispatcher. Only one is required and if both are present then they can be in any order.

Example: @AWS,1000 {set shutter acceleration ramp time to 1000 ms}.

Any unrecognised or invalid command responds with the text :Err#.

In general, responses always begin with : and end with #.

Unless otherwise stated in the table below, all commands respond by echoing their command code and target device, in the format:

: cct #

where cc is the original command verb and t is the target device ('R' for rotator, 'S' for shutter).

The parameter value (if any) is not echoed. For example, the response to @GAR,1000 is :GAR#. Receipt of this echo response indicates that the command is valid and was successfully received.

Commands that return a value include the value immediately after the target and before the terminating #. Example: :VRR10000#

Any command that cannot be processed for any reason will respond with :Err#

Other status and debug output may be generated at any time, not necessarily in response to any command. See Event Notifications below.

In the following table, upper case letters are literal characters. Lower case letters are placeholders. Unless otherwise specified, the range of step values is 0 to 4,294,967,295 (2^32 - 1). Due to firmware resource constraints, range checking for "sensible settings" is left to driver and application developers. If in doubt, the ASCOM driver (open source) serves as a reference implementation.

This table is valid for firmware version 4.0.0 or later.

Cmd	Targets	Parameter	Default	Min	Max	Response	Example	Description
AR	RS	none				:ARtddddd#	@ARR	Read acceleration ramp time in milliseconds
AW	RS	ddddd	1500	100		:AWt#	@AWS,1000	Write acceleration ramp time
BR	S			0	1023	:BRSdddd#	@BRS	Read battery low voltage threshold in ADUs
BW	S	dddd	0	0	1023	:BWS#	@BWS,890	Write battery low voltage threshold in ADUs
CL	S					:CLS#	@CLS	Close the shutter (see event notifications)
DR	R	none				:DRRddddd#	@DRR	Read Dead-zone in steps (153 steps = 1 degree)
DW	R	ddddd	300	0		:DWR#	@DWR,300	Write Dead-zone in steps [0..10000] default 300
FR	RS	none				:FRstring#	@FRR	Reads the semantic version (SemVer) string of the firmware.
GA	R	ddd		0	359	:GAR#	@GAR,180	Rotates to the specified azimuth in the shortest direction.
GH	R	none				:GHR#	@GHR	Calibrate rotational positioning by rotating clockwise until the home sensor is detected.
GS	R	ddddd		0	@RR	:GSR#	@GSR,1000	Rotates to the specified whole step position in the shortest direction.
HR	R	none				:HRRddddd#	@HRR	Home position Read (steps clockwise from true north)
HW	R	ddddd	0	0	@RR	:HWR#	@HWR,1000	Home position Write (seps clockwise from true north)
OP	S					:OPS#	@OPS	Open the shutter (see event notifications)
PR	RS	none				:PRt-dddd#	@PRR	Position Read - get current step position in whole steps (signed integer)
PW	RS	ddddd		0	@RR	:PWt#	@PWR,-1000	Position Write (sync) - set step position
RR	RS	none				:RRtdddd	@RRS	Range Read - read the range of travel in whole steps.
RW	R	ddddd	55080	0		:RWR#	@RWR,64000	Range Write (Rotator). Sets the dome circumference, in whole steps.
RW	S	ddddd	46000	0		:RWS#	@RWS,64000	Range Write (Shutter). Sets the maximum shutter travel in whole steps.
SR	RS	none				:SEt,...#	@SRR	Requests an immediate status report. Status returned as comma separated values.
SW	RS	none				:SWt#	@SWS	Performs an immediate "hard stop" without decelerating.
VR	RS	none				:VRtddddd#	@VRR	Velocity read - motor speed in whole steps per second
VW	R	ddddd	600	32		:VWR#	@VWR,10000	Velocity Write (Rotator) - motor speed in whole steps per second
VW	S	ddddd	800	32		:VWS#	@VWS,10000	Velocity Write (Shutter) - motor speed in whole steps per second
ZD	RS	none				:ZDt#	@ZDR	Load factory defaults into working settings (does not save)
ZR	RS	none				:ZRt#	@ZRR	Load saved settings from EEPROM into memory
ZW	RS	none				:ZWt#	@ZWR	Write working settings to EEPROM
ZZ	RS	none				none	@ZZR	Reboot the microprocessor (note: there are reports that this is not reliable).

The firmware will produce notifications of various events that can happen whether or not the application is requesting them. These may arrive at any time, for example in between a command and a response, but they will never divide a response. Client software must be prepared to handle these event notifications at any time.

Format	Description
XB->{state}	The current state of the XBee communications link. The states are enumerated below.
XB->Start	Waiting for XBee to boot up or reboot
XB->WaitAT	Waiting for XBee to enter command mode
XB->Config	Sending configuration
XB->Detect	Attempting to detect the shutter
XB->Online	Communications link established
Pddddd	Rotator position (ddddd = signed decimal integer)
Sddddd	Shutter position (ddddd = signed decimal integer)
:SER,p,a,c,h,d#	Rotator status report. Sent when the rotator motor stops or when requested by @SRR
	p = current azimuth position in whole steps,
	a = Homed (1 = homing successful, 0 = homing failed)
	c = dome circumference in whole steps
	h = home position sensor location, in whole steps clockwise from true north
	d = dead zone (smallest allowed movement in steps)
:SES,p,l,o,c#	Shutter status report. Sent when shutter motor stops or when requested by @SRS
	p = position in steps
	l = limit of travel (fully open position) in steps
	o = state of open limit switch, 1=active, 0=inactive
	c = state of closed limit switch, 1=active, 0=inactive
:left#	The rotator is about to move to the left (counter-clockwise)
:right#	The rotator is about to move to the right (clockwise)
:open#	The shutter is about to move towards open
:close#	The shutter is about to move towards closed
:BVddddd#	Shutter battery volts in raw analogue-to-digital units (ADUs), range [0..1023].
:Rain#	Rain detected (shutter will auto-close)
:RainStopped#	Rain detector was previously indicating rain but has now stopped doing so.
:Volts#	Emitted every ~30 seconds while shutter battery voltage is below the configured threshold set by @BWS.

Position updates occur about every 250 milliseconds while motion is occurring. When motion ceases, an SER or SES status event is emitted and this indicates that motion of the corresponding motor has ceased.

Important: Don't assume that the motors will only move when requested by the application. Motors can move for a variety of reasons, including:

• because the user is pressing the toggle switch
• a weather shutdown event
• shutter auto-close on low battery

If that happens, all the normal events will be sent, including direction notification, position updates and finally a status report when the movement stops. Therefore, applications must be prepared to accept event notifications even if they are not currently requesting anything.

Read this carefully - it will have implications for client application design

It is a near certainty that other undocumented output may be produced and the host application must be constructed in such a way that this output is ignored. Undocumented output will change from version to version, so do not rely on any observed undocumented behaviour.

Undocumented/Diagnostic output should not be relied upon by a client application for any purpose as it may change without notice.

Different firmware versions support different features. When using these features, clients should read the firmware version (@FRR, @FRS) as a first action and adapt appropriately.

Introduced	Deprecated	Feature
3.4.0	-	Shutter Auto-close on low battery volts (@BRS, @BWS)
3.4.0	-	:Volts# low battery notification
3.2.0	-	High Precision Slew to step position (@GSP)
3.0.0	-	All other features herein documented