Serial API

Command	Description
"M <id> ON\n"	power up the motor
"M <id> OFF\n"	power off the motor
"M <id> HOM\n"	perform homing sequence
"M <id> ABS <steps>\n"	move motor to absolute position in
"M <id> REL <steps>\n"	move motor by relative from current position
"M <id> SPD <speed>\n"	set maximum speed in steps per second
"M <id> ACC <acceleration>\n"	set acceleration in steps per second^2
"M <id> SG <sgthresh>\n"	set SG THRESHOLD value of TMC2209 driver (used for stallguard)
"S ON\n"	power on the servo
"S OFF\n"	power off the servo
"S IN\n	turn the servo from the optical axis (hide the neon)
"S OUT\n"	turn the servo to the optical axis (show the neon)
"R ON\n"	turn on the relay
"R OFF\n"	turn off the raley