How many I/O and what are they for.???

[JAZZCNC]

So let's start with How many I/O.? ( or Inputs & Outputs for those who are brand, brand new and thinking let's start with WTF does I/O mean...Lol)
With the term I/O I'm talking about General Inputs and Outputs which we can use for machine control and not MOTOR OUTPUTS which are slightly different but can be used for I/O in some controllers but I won't go into that here.!

I'm also working based on a Router but a Mill isn't much different.

Ok well, the simple answer is you don't actually need any in most cases.? The machine can be set up so it will quite happily to work without talking or receiving messages from the outside world.
However, that wouldn't be very safe so as a minimum you need at least 1 INPUT so an E-stop signal can be sent to the INPUT when you hit the "Oh Shite" Button.!

Next, you might want LIMIT switches.?
These can be wired in several ways depending on switch type etc ie: series or parallel and how the builder wants them to work on the machine. Each way will use a different number of INPUTS. This can range from 1 INPUT for the whole machine or between 1-2 per axis.
For instance, if you use simple micro switches and are limited on I/O you would use 2 SW per axis (+/-Limits) and wire ALL SW in a series connection which would only require 1 INPUT. If any 1 switch trips then ALL axis will show a LIMIT as tripped.

At the other end of the extreme, you could have an SW for each end of travel, so each SW would require an INPUT so for typical 3 Axis machine that would be 6 inputs.! However, this would show which Axis tripped and which end of travel.

In practice you would most likely use 2 SW per axis wired in series and use 1 IN. Totaling 3 INPUTS for 3 axis machine. This setup would show which Axis Tripped but not which end of travel.
OR you can have just 1 SW which travels with the axis and looks for a target at each end of travel. This still requires 1 INPUT but with only 1 SW, it still only shows which axis tripped and not which end of travel.

Then you might want HOME switches.?
This would require 1 INPUT per axis and if it's a 3 axis machine that uses slaved motor effectively making it 4 Axis then you would need 4 SW each using an INPUT if you want to square up the gantry.

Now if I/O is limited then it is possible in some cases to combine HOME and LIMITS so they use the same SW. This does mean however that when homing the LIMITS will be turned OFF so it's a little less safe. Usually, with a stepper system, this isn't a problem because you HOME slowly and the motors will stall if something goes wrong. However for instance with a Servo driven machine then if they decide to take off then all hell could break loose and you are not protected by the LIMITS so you would fit separate home SW.

So lets do a quick count up.
2 I/O = E-stop and series wired limits.
4 I/O = E-stop, with limits per axis or combined homes and limits
5 I/O = E-stop and Slaved motors with shared home/Limits.
7 I/O = E-stop, per axis Limits, per axis Homes.
8 I/O = E-stop, per axis Limits, per axis Homes with slaved motor gantry using squaring.
10 I/O = E-stop, per axis Limits, per end trip, per axis homing.
11 I/O = E-stop, per axis Limits, per end trip, per axis homing with slaved motor gantry using squaring.

A typical above basic but safe machine will use 4 or 5 INPUTS depending on 3 or 4 axis.

The next post will be about OTHER INPUTS, I'll get to OUTPUTS later.

EDIT: I forgot to point out that it is possible to use limits and homes with just 1 INPUT but it's not recommended because it means using NO (normally open) switches and that's not safe for the limits because if a wire breaks you won't know about until the machine crashes when they don't work.!!