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Revision to Connecting endstop switches

David Crocker

* An endstop switch with an active-low output holds the input pin at about 3.3V when the switch is not triggered, and about 0V when it is triggered. One example is a normally-open microswitch (which is not recommended, because a normally-closed switch is safer). Another example is a Hall sensor with an open-drain output that is connected directly to the Duet endstop input. The LED on the Duet will be illuminated when the switch is connected and triggered.
 
The endstop switches each need to be able to sink 1.5mA current for the Duet 2 WiFi and Duet 2 Ethernet, 0.3mA for the Duet 2 Maestro, and 2.1mA for the DuetDuet 06 or 085. This is not usually a problem, except with some optical endstop switches that were not designed properly for 3.3V operation.
The endstop switches each need to be able to sink 1.5mA current for the Duet 2 WiFi and Duet 2 Ethernet, 0.3mA for the Duet 2 Maestro, and 2.1mA for the DuetDuet 06 or 085. This is not usually a problem, except with some optical endstop switches that were not designed properly for 3.3V operation.
 
Each axis endstop input can be configured in firmware for a Max (high end of axis) or Min (low end of axis) endstop, and with an active high or active low signal level. Configuration is done in config.g using the M574 command.
 
Note: opto endstops made to the Generation 7 design are often claimed to be 3.3V-compatible, but in fact the design is marginal with a 5V supply and frequently doesn't work at all on 3.3V. To use this design with a 3.3V supply, you may need to replace the 180 ohm resistor by 100 ohms, and either replace the 1K resistor by 10K or remove it completely.
 
The Duet 2 Maestro has 30V-tolerant endstop inputs, so if your optical endstops do not work with a 3.3V supply then instead of modifying them you can provide them with a 5V supply instead and connect the outputs of your endstops directly to the STP pins of the Duet 2 Maestro.
 
== Test endstop switches ==

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