flexi-bot/docs/marlin/_gcode/M512.md

tag	title	brief	author	since	requires	group	codes	related	notes	parameters	example
m0512	Set Passcode	Set a numeric passcode for locking the machine	shitcreek, thinkyhead	2.0.6.1	PASSWORD_FEATURE	security	M512	M510 M511	Requires `PASSWORD_FEATURE`. Use `PASSWORD_LENGTH` to configure the length, up to 9 digits.	tag description values P Current passcode. This must be correct to clear or change the passcode. tag type password int tag optional description values S true If `S` is included the new passcode will be set to this value. tag type password int	pre code Change passcode from '1234' to '9090' M512 P1234 S9090

Check the passcode given with P and if it is correct clear the passcode. If a new passcode is given with S then set a new passcode.