Spindle On/Off setup?

Hello,

I did a quick search but didn't really come up with anything exact. I was wondering how I can turn on/off the spindle via gcode? I currently have a gecko drive (g540) with one of the output (pin 5) connected to the run input of the SuperPID. This is a known configuration from SuperPID so it should work. The question is setting it up on linuxcnc.
Under the configuration wizard of linuxcnc where I setup the parallel port, I used one of the pin (I think pin 17.... not sure) I set this to "Spindle On". The question is, which g-code will turn on that pin. M3 and M4 is used as CW and CCW on the spindle and M5 is to stop the spindle. Which G-code is for "Spindle On"?
Also if using M5 command, does that turn off the M3 and M4 if they are setup to be used?