Author Topic: PMDX 411 output signals help  (Read 1900 times)

DJS

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PMDX 411 output signals help
« on: May 17, 2020, 02:37:54 AM »
I'm using Mach4 and a PMDX-411 to run a small CNC mill.  I have qty 3 Gecko drive 203V drivers to run the axis on the mill.  I had the whole system working for years with Mach3 and a parallel port but my computer's hard drive died and I was forced to upgrade to Mach4 and a PMDX-411.  I was able to get the PMDX-411 working with Mach4 enough to jog all the axis and run a simple G-code.  Now I am try to get the Machine Disable button working.  The Enable/Disable button on Mach3 would also enable or disable my 203V drives. When Enabled - the stepper motors were energized and ready to be run by the computer program.  When Disabled - The stepper motors were de-energized and the axis' could be moved with the hand wheels on the mill. 

In Mach4 I have mapped the Machine Enable output to pin 1 of the PMDX-411.  This is then wired to all 3 of the 203V drives.  The problem I am having is that the 203V drive are disabled when the signal on pin 1 is high (5V) and Enabled when the pin 1 is low (0V).  This is backward from what I need.  Currently when I push the enable button on Mach 4 the drives are disabled and then when I press the disable button on mach4 the drives are enabled.  I thought I could just go back into the contorl configuration in Mach4 and green check the active low button to fix the problem but when I do that the output stops working and stays low all the time.  Therefore the 203V drives are never disabled.
 When I check the PMDX-411 I/O status and toggle the enable button in Mach 4 I see the same thing...  When active low is not checked in the configuration control the output toggles (albiet the opposite polarity that I need.)  When active low is checked the output stops toggling and just stay low.  Any idea how I can get the output (using pin 1 of the pMDX) to be low when Mach4 is enabled and high when Mach4 is disabled?  Mach3 did this the way I need it without any issues.

12strings

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Re: PMDX 411 output signals help
« Reply #1 on: May 18, 2020, 01:31:45 PM »
I think you will need an external switch to control the G203V's ENABLE input.

When Mach4 is "disabled", the PMDX plug-in and firmware do not allow controlling any output signal.  All step/dir remain idle and all non-step/dir pins are driven low.  So having an active low signal that is asserted only when Mach4 is disabled won't work - as you found out.

There is a drawback to having the motor drivers disabled every time you disable Mach4.  Every time you disable the motor drivers, there is a chance that the motors will cog to a slightly different position.  See https://faq.pmdx.com/index.php?solution_id=1008.

DJS

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Re: PMDX 411 output signals help
« Reply #2 on: May 18, 2020, 11:55:51 PM »
Ok thank you for the help,  Does Mach 4 work differently in this regard to Mach 3?  I had the whole setup working in Mach 3 just this way.  Either way I can wire a seperate switch to the line and get the system working.

12strings

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Re: PMDX 411 output signals help
« Reply #3 on: May 21, 2020, 11:26:25 PM »
This is not strictly a Mach3 vs Mach4 thing.  It is the way PMDX appears to have designed their devices vs. the way the Mach3 parallel port (appears to have) behaved when Mach is "disabled".  It looks like maybe the PMDX-411 drives the output signals low when Mach4 is disabled, even if it is configured as active low.  Perhaps they figured this was s safest option.  Or perhaps it was an oversight handling the enable signals.