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Power Management
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Power management is used to keep the steppers on when you need them and turn them off 
when you don't. Stepper motors consume maximum power when idle. They hold torque and
get hot. If you shut off power the motor has (almost) no holding torque. Most lead 
screw or geared machines will hold position if you shut off the power when the motor 
is not moving, but belt machines generally do not.

In either case it's usually a good idea to keep all motors powered during a machining
cycle to maintain absolute machine position. Depending on your machine you either may
want to remove power some number of seconds after the machining cycle, or leave the 
motors powered on for as long as the machine is on.

You also generally want to use power management to de-power the machine if it's left 
unattended for an extended time. You don't want to leave the steppers on for extended 
idle times such as walking away from your machine and leaving it on overnight with the
motors idling.

The power management commands let you set up the right set of actions for your machine
and use. Per-Motor Commands

Setting    Description 	Notes
 1PM = 0   Always disabled
 1PM = 1   Always enabled
 1PM = 2   Enabled in cycle
 1PM = 3   Enabled while moving

These commands affect all motors and take effect as soon as they are issued.

Motor Disabled (0)
This will turn off motor power and prevent the motor from turning on. 
Disabling the motor will prevent that axis from participating in any move. 
The motor will not be affected by ME or MD commands. This setting takes effect 
immediately.

Motor Always Powered (1)
This will turn on motor power and leave it on until the board is shut down. The motor 
will not be affected by me or md commands. You generally do not want to use this mode
as it will leave the motors on for extended periods of time if you do not power down 
the machine. Better to set a long motor power timeout and use Powered In Cycle (2)

Motor Powered In Cycle (2)

This will turn on the motor power at the start of any move on any axis (a "cycle"), 
and will de-energize the motors mt seconds after the cycle is complete (all motion 
stops). The timeout interval is set by the mt value (see Global Power Management 
Commands). 

Motor Powered When Moving (3)
This will turn on the motor power only when that axis is moving, and will remove power
mt seconds after that axis stops moving.
