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Author Topic: A Puzzler: Is the Parallel Pin connected to the GND side or the PIN# side?  (Read 3063 times)

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I've got a bit of a puzzle that I've spent a few days on and can't for the life of me solve...  I can't work out wither the Parallel Pin is connected to the GND side or the PIN# side of the BoB for any particular pin - it seems to be connected to both (sort of).  Here's what I mean:

I've got the zeroing on my machine working.  I've wired the XYZ homing-plates into the GND terminals on the BoB for each pin.  I use a common wire for the crocodile clip (that attaches to the cutter) that goes to the PIN# terminal of Z.  It works...

However I was under the impression the PIN# terminal (which is at +5V relative to connection marked GND making me believe it's held high) should also work - i.e. the reverse of the above, but it doesn't.  Mach3 seems to auto-set the pin numbers correctly and sets them as active high (I think the ZP5A BoB might be inverting the signals?) but when I run the same auto zero code it doesn't work.

I just can't understand what is happening - whether the Pin is held high (and is connected to the terminal connection marked PIN#) or whether the Pin is held to ground and is actually connected to the GND terminal.  Because Mach3 auto-sets the same either way, but just doesn't work via the auto-zero command I'm well and truly at a loss!

I've attached a (badly drawn!) diagram in the hope this helps me explain!  (The G is GND and the P is the appropriate PIN# terminal at +5VDC relative to the GND)

Oh, and I also understand the theory behind active low/high for both NC and NO but with this BoB Mach3 doesn't set as the theory suggests.  For example the Estop is connected NC directly through the PIN# and GND terminals of a pin but when the switch is opened Mach3 see's it as active low.  I was of the belief that it should be active high (so the pin is held low whilst switch is closed and then goes high when the switch is opened).

« Last Edit: February 11, 2014, 12:47:08 PM by mattnedgus »

Offline Fastest1

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A Puzzler: Is the Parallel Pin connected to the GND side or the PIN# side?
« Reply #1 on: February 25, 2014, 07:45:49 AM »
Check or uncheck active low and see if the status changes when testing. Low is sinking the circuit to ground, High is sourcing the 5v. That is my understanding. I don't use auto set up.

On my EStop port 1 pin 10, switch is an NC, active low unchecked. It will have 5v present til the EStop is pressed. Then it will go low and trip Mach.
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Re: A Puzzler: Is the Parallel Pin connected to the GND side or the PIN# side?
« Reply #2 on: February 25, 2014, 09:22:07 AM »
Your first drawing uses one pin so presumably you have each of the three home pins set to that pin number. Your second drawing uses three pins so you have each home pin then set to those three pins - yes?

Re: your E-stop - something is not as it seems - are you sure it's a NC?

If in doubt - please post your xml and autozero button code.
Re: A Puzzler: Is the Parallel Pin connected to the GND side or the PIN# side?
« Reply #3 on: February 26, 2014, 05:17:21 AM »
Thanks for you replies!

I'll have a look again later at the system now that I have (just arrived!) the relay and parts to set up a better (and hopefully working!) limit switching system.

From what I could tell though and because the homing only worked as per the original diagram I'm left to believe that the labelling on the breakout board is wrong or something beyond my comprehension is happening.  I tried the active low/high swapping before with no luck.  I was left to assume that the breakout board is either inverting the signal Mach3 receives (so what I read is the opposite of what is happening at the parallel pin) or the pin is actually held to ground - for now if it works after I've fiddled with the limit switching system I think I'll leave it and not worry too much (I just really like to understand exactly what's going off!).