MSO — Motion Servo On

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Description

MSO (Motion Servo On) enables the drive of an axis. On a stepper axis it asserts the driver’s Enable pin so the motor is energized and holds position; on a DC axis it arms the H-bridge; on a servo axis it marks the axis ready. It sets the axis member DriverOn and nothing else. Use MSO once at power-up or when the machine is put into run, before any MAM, MAJ or MAG on that axis. Do not use MSO to start motion; it energizes the motor and leaves it where it is. An axis whose driver has no Enable pin wired is always energized, and MSO on it only sets the status bit.

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Operands

Operand	Type	Format	Valid Range	Required	Description
Axis	Axis	Axis name	Any axis in Explorer ▸ Axes that has a driver	Yes	The axis to enable. An axis without a driver is a build error.

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Scan Behavior

Prescan

Nothing. DriverOn is 0 at power-up; every axis starts disabled.

Rung-condition-in is false

Nothing. The axis stays in whatever state it was left.

Rung-condition-in is true

The driver is enabled and DriverOn = 1, on this scan and every scan the rung stays true. Repeating it changes nothing, so MSO may be held true or pulsed.

Postscan

Nothing. The driver stays enabled until an MSF runs or the controller resets.

Axis type	What MSO does
Stepper (step/dir, TMC2130, 4-wire)	Asserts the Enable pin; the motor is energized and holds.
DC (L9110S H-bridge)	Arms the bridge; an MAJ may now apply duty.
Servo	Sets DriverOn only; the servo library holds the last angle regardless.

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Axis Members

Motion status lives on the axis, not on a per-instruction tag. Every member is a reference you can use anywhere (XIC Feed.DriverOn, MOV Feed.ActualPos Pos_Now).

Member	Data type	Set by	Cleared by	Description
DriverOn	BOOL	MSO	MSF	The drive is enabled. This is the member MSO writes.
EN	BOOL	MAM, MAJ, MAG while a command is active	Command complete, MAS, MSF	A motion command is engaged.
IP	BOOL	Axis service while steps are being produced	Motion stops	Motion in process.
DN	BOOL	MAM reaching its target, MSR	Next MAM or MAJ	Instruction done.
PC	BOOL	Same as DN	Same as DN	Process complete.
InMotion	BOOL	Axis service	Axis service	Steps produced this scan.
Dir	BOOL	Axis service	Axis service	1 = forward.
Error	BOOL	Watchdog mismatch, TMC2130 driver fault	MAFR	Axis fault.
ActualPos	REAL	Axis service every scan	—	Position in axis units (counts ÷ counts per unit).
CmdPos	REAL	MAM, MAG, MSR	—	Commanded target in axis units.
Counts	DINT	Axis service every scan	MSR, ResetCounts	Raw step counts.
RedefinePos	REAL	MSR	—	Value of the last MSR.
ResetCounts	BOOL	Your logic (write 1)	Firmware, after zeroing	Zero the counts without an MSR.
Watchdog	INT (ms)	Axis properties; your logic may overwrite	—	How long commanded and actual motion may disagree before Error sets.

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Example

Scenario: A two-axis feeder. One selector switch, Servo_On, energizes both axes so the operator has a single “drives on” control.

Tags and axes:

• Servo_On — Servo on, BOOL
• Feed — stepper axis, step/dir driver on D8/D9, 80 counts per mm
• Follower — stepper axis, step/dir driver on D6/D7, 80 counts per mm

Rung 1:

—|XIC Servo_On|——┬——[MSO Feed]——————┬——
                 └——[MSO Follower]——┘

Scan 1 — Servo_On = 0. Both drives disabled. Feed.DriverOn = 0, Follower.DriverOn = 0.

Scan 2 — Servo_On = 1. Both blocks execute. Feed.DriverOn = 1, Follower.DriverOn = 1. Motion blocks paint neutral; the lit wire shows the rung is true.

Nothing moves yet. The MAM, MAJ and MAG pages carry on from this state.

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See Also

• MSF — Motion Servo Off (the opposite)
• MAM — Motion Axis Move (the usual next instruction)
• MAFR — Motion Axis Fault Reset
• Adding an Axis — driver, pins, units and counts per unit
• Motion Instructions — Category index

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Notes

MSO first, always. A move or jog commanded while the drive is off is still counted. The step pulses go out, the counter advances, ActualPos changes, but the de-energized motor never turns. The controller then believes the axis is somewhere it is not. Interlock every MAM and MAJ with XIC <axis>.DriverOn.

Holding torque. With the drive enabled a stepper holds its position and draws current standing still. MSF releases it.

No Enable pin. A step/dir driver with the Enable pin left blank in the axis properties is wired always-on. MSO and MSF then only change DriverOn; the motor is energized from power-up.

One instruction per axis. MSO takes one axis. Enable several with an output branch, as in the example.