pins going high on boot up for around 10 seconds

Hi All, I wanted to see if anyone has come across this before:

When I boot the computer, before Linux even starts up, the DB25 pins go high for a few seconds, maybe 10.

This causes an issue in my system because I use relays on two of the pins to activate a couple devices. When the pins go high, it activated my relays which activates the devices if they are powered up. This is a low cost industrial automation machine that will be put in a production environment. This isn't a safety issue, but it can create a mess because one of the devices is a dispenser.

This only happens if the devices are powered up before the computer is booted, but I'd rather not have to rely on a start up procedure to prevent this.

Is there a known solution to this? Maybe a BIOS setting that skips this port check or something? Or a different wiring solution?
Any help would be GREATLY appreciated!


Here's the system:
single axis stepper on a ball screw linear actuator
2 devices activated by closing a circuit (connecting two pins together on their individual IO ports)
I use the coolant M codes to activate these in the program.
Pins from DB25 cable are connected to relays which close the circuits activating the two devices.
Relays are the 4 terminal, low voltage type.
Devices were previously triggered by foot switch.

What breakout board are you using? Some have provisions for a charge pump or a safety/enable circuit.
Have you checked all other available output pins on the port? Some may behave differently on startup.

Thanks Andy, I'm going to have to research charge pumps and wiring. This is new to me.

Todd, actually, I'm not using a typical breakout board. I'm using a D25 feedthrough module from automationdirect.com

ZIPLink communications feedthrough module, 25-pin male and female D-sub connectors to terminal blocks, 35 mm DIN mount.

I'd rather be using a breakout board as they are opto isolated. I actually ordered one, but could not get it working. I'm not sure if its defective, or if I just wasn't understanding something. It was obviously designed for Mach 3. Here's what I have:

KL-DB25-5, BREAKOUT BOARD WITH OPTICAL ISOLATED FOR STEPPER MOTOR DRIVER MACH3,WITH RELAY AND PWM SPINDLE CONTROL

I don't know what you may have done wrong with that board. Did you have 5v power to it? How did you have it hooked up? Looks like it is set up for sourcing inputs and sinking outs.

I've had good luck using CNC4pc C10 boards. They have an enable circuit. (CNC4pc also sells a charge pump contraption, but I've never used one.)

Thanks! This is resolved now. I've now built two machines using CNC4PC C11S boards and separate charge pumps. It has been really easy actually. The charge pump doesn't get enabled until linuxCNC is running.