TIPS FROM THE EXPERT Date: 28 Jan 2026
Inverting Outputs
When it comes to configuring outputs here is a simple rule of thumb.
If at all possible do not invert an output
As with all rules they are made to be broken and sometimes it is unavoidable but let me explain why inverting an output is not a good idea in many cases
Output Logic
As you will be aware output logic can be inverted simply by selecting the output in the F1 screen and pressing the space bar. Normally when an output is turned on it will go high sending a 5 volt signal to the external device and when it is turned off it will send 0v to the device. When you invert the logic the output will now send 0v to the external device when it is turned on and 5v when the output is off. Note that the on / off functionality of the output does not change but the output signal is not the inverse of what it is normally.
The Problem
This sounds very straight forward and will work very well but there is a small problem. The normal state of a MASSO output at power on is Low (0 volts) until the controller is fully powered up and running which takes about 5 seconds at which time it will set the output status to match the system configuration. This behavior is true of all control systems so you need to take this into account. In some cases it may not matter while in others it may matter a lot.
Tool Tray
Imagine you are doing a machine conversion where you use a MASSO relay to operate the original tool tray circuit. When the MASSO relay is off the tool tray moves out and when the MASSO relay turns on the tool tray moves back and you need it to work the opposite way. To fix this I could invert the MASSO output. The problem is when powering up, the tool tray will move out and then a few seconds later the tray will move back to its normal location. This will not do and I don’t want to rewire the entire original tool tray circuit.
Solution
Instead of using the normally open contacts on the MASSO relay to operate the tool tray I can simply use the normally closed contacts and not have to invert the MASSO output at all. The relay inverts the signal for me without the need to invert the MASSO output at all. The tool tray does not need to be touched and it no longer shoots out and back in when the controller is powered on. When using the MASSO relay changing from the normally open to the normally closed contact and vice versa is the same as inverting the MASSO output but without the problems.
Laser
I have an engraving laser which turns off when it receives 5 volts and on when the voltage is 0. It was a very poor design. To make it work as it should I need to invert the MASSO output after which it will work perfectly except when the machine is powered up. On power up the MASSO output will be 0 volts so the laser will turn on and burn anything that is in its path until the controller starts and the inverted output starts outputting the inverted 5 volt signal.
To fix this there are 2 solutions.
- Modify the laser input circuit so that the laser turns on with 5 volts and off with 0 volts. This removes the need to invert the output and the laser will not turn on unexpectedly at powerup and everything will work correctly.
- Wire the Laser so that it does not get power until the laser receives an enable signal. While the laser still needs to have the output inverted to make it work correctly the laser will not turn on at power up until the user is ready for it by which time the MASSO output is in the correct state. This can be as simple as using a MASSO Auxiliary output and MASSO relay to provide power to the laser. The M64 & M65 Gcode can be used in Gcode to automatically enable the laser from Gcode or an auxiliary toggle input can be used to manually enable and disable the laser with the push of a button before using the Laser.
If you cannot modify the laser then using the enable relay solution is one of those exceptions to the rule where you need to leave the output inverted but having thought about it and understanding the problem at power up you can remove it by making sure the laser is not powered on until MASSO is fully powered up and you are ready for it.
So next time you are thinking about inverting an output on your MASSO stop and ask yourself, do I really need to invert this and what will happen at power up then the output will be 0 volts? Will it cause strange behavior or will it have no effect?
For more from MASSO, see what’s new at masso.com.au or email us on newsletter@masso.com.au
MASSO CNC Australia, Ingleburn, NSW, 2565, Australia, masso.com.au
