7i43 Input Pull-Ups

02 Oct 2011 01:07 #13592 by photomankc
I'm afraid I know the answer here and I'm really going to be unhappy but is the Mesa board pulling all my inputs up with no ability for me to stop it? My E-Stop circuit is not active high, nor did it really make sense to me for it to be so when I was making it, but it apears the Mesa is pulling the input for sensing the EStop circuit high so that when I connect my switch and press it to break the 5V line that supplies it instead of being pulled down to ground as it was designed it's splitting the voltage between my pull-down and its pull-up. That's a bit agrevating. I really don't like when something I hook up to sense the condition of something goes off and desides what it's condition should be.

I can understand the pull-ups on outputs. I don't understand it for inputs. The rest of the circuit should be deciding what the input is supposed to be.

Please Log in or Create an account to join the conversation.

02 Oct 2011 03:06 #13594 by PCW
Replied by PCW on topic Re:7i43 Input Pull-Ups
All 7I43 pins are pulled up. Its for compatibility with I/O module racks (which are active low)
and because the only pre-configuration option on FPGA pins is pullup or no pullup.
This is described in the STARTUP STATE section of the 7I43 manual.

If you want a defined state on all pins all the time, and want to drive standard current sinking type OPTO loads (Like OPto22 etc) its really the most practical solution.

I agree that an active high estop is not the most desirable thing, but since you have a 5V system
you can use a stout pulldown (say 200 Ohms so) to solve the issue or edit the .UCF file and remove the pullup from the pin used for ESTOP

Please Log in or Create an account to join the conversation.

02 Oct 2011 03:38 #13595 by photomankc
Replied by photomankc on topic Re:7i43 Input Pull-Ups
Yeah I had read that section but it mentioned that the pull up or pull down are set in the firmware and I figured it would not pull up an input but I guess I can see why given most are interfacing directly. I definately don't like pulling estop's defualt to the not-estopped state Anyway, the EStop circuit was set and designed before I had the Mesa. It would be a bear to change the pull downs and polarity of it all. I thought my pulldowns were stout at around 2.4K! Dang it.

I can get around this, though not ideally, by taking the EStop indicator LED signal and inverting it's meaning and feeding that to the Mesa card. Just means I have to add a positive rail for the LEDs and connect the cathode to that output.

Assumption, it's the mother of all ..............

Please Log in or Create an account to join the conversation.

Moderators: PCWjmelson
Time to create page: 0.098 seconds
Powered by Kunena Forum