There is only one pulse from TCNC. You can set how long this pulse is going to be though.
So if you want to change tool, you will either have to place the next tool to use on the upcomming slot, or write several M6 commands. I'm trying to place the next tool I'm using in the next slot. If thats not possible, I will just have to repeat the M6 command a couple times..
I have been toying with the idea of making a separat tool changing computer (just a microcontroller with LCD display and a simple keypad) which keeps track of what tool is to be used next and so indexes to this tool. My tool changer is already controlled by a microcontroller, so adding a feature like this should not be too hard.