BBB not booting if connected to Motor Controller MD10C

Hello All,

I have become stumped by this issue. I am trying to boot up a BBB when connected to the inputs of six MD10C motor controllers. For the most part, it works fine if the BBB has been boot up before connecting the direction and pwm pins to the beagle bone black. If I attempt to power the BBB with them connected, the power light indicator will come on, but the status lights will not. The configuration of the circuit is this: I have a custom shield that I made that breaks out the pwm pins and gpio pins I need for the controller. The controllers are powered by an 24V battery power supply rated at 15A output. The BBB is powered by 5V regulator rated at 6A.

Here is what I have attempted thus far:

  1. Turn on battery, which is powers the 5V regulator and the motor controllers, which turns everything on at the “same” time. BBB does not boot up.

  2. Remove cape (with all the connections still on), turn on battery, BBB boots, once the light indicators are no longer all a solid blue, I replace the cape, and everything works, BBB continues to boot up.

  3. If I remove all but one input to one controller and power up the battery, BBB sometimes boots.

  4. I have attempted to add 1k and 10k resistors between the connections which allowed the BBB sometimes to boot with two motors inputs connected.

  5. Wierd one: I decided to remove the power from two controller (except for ground), and connect them to the BBB. Still it did not boot. The motor controllers did not get powered at all!

  6. Wierder one: I removed all of the power wires from from both controllers and still the BBB will not boot up if connected to the motor controller inputs.
    Does anyone have idea what is happening here? One of my solutions was to use a relay to turn on the power to the motor controllers after the BBB has fully booted up or add a second switch that turns on the motor controllers after the BBB has fully booted, but that plan can not work if merely pluggin in the inputs causes this problem.

I do know about this issue: DO NOT APPLY VOLTAGE TO ANY I/O PIN WHEN POWER IS NOT SUPPLIED TO THE BOARD. IT WILL DAMAGE THE PROCESSOR AND VOID THE WARRANTY. NO PINS ARE TO BE DRIVEN UNTIL AFTER THE SYS_RESET LINE GOES HIGH. But in this case, there is no power coming from the input pins.

Last note: I measured the resistance from the dir pin and the pwm pin to ground and they come up 16k and 20k respectively.

I appreciate any suggestions or help on this matter.

The Sitara uses a field of pull-up and pull-down resistors to tell it how to boot.
If you put any LOAD on these pins, and your I/O does NOT have to be powered, (which would make
things even worse), you will give it the wrong boot commands, and the BBB won’t boot.

Go read the section in the System Reference Manual on Boot Configuration, and
the section on Pin Usage Considerations.

— Graham

Thank you Graham. That clears a lot of stuff up for me. It just so happens that I am using 8 of the LCD data pins for my shield without knowing about how loading those pins down can result in a disturbance in the booting process. Since I was not using an LCD, I thought no harm would come from using those pins.

My advice is to read the System Reference Manual. It will save you a lot of heartache.

Gerald