Some GPIOs don't work ?

Hello guys,
I’m working on BBB for a school project. I need to control 6 motors with my BBB.
But it seems that some gpios don’t work. When I test them with an oscilloscope as output they aren’t all detected and some of them don’t change from 0V to 3.3V when I change value from 0 to 1.
Could it be the pin mode who affects it ?
I’m completly lost, could you help me ?
Thank you in advance.

Not every pin is muxed as GPIO/Mode 7. You have to pinmux them if you want to use it as GPIO pin. And even some pins cannot be pin muxed as GPIO; they are GND, 5V, 3V3, and analog input pins.

Hello guy,

as Sungjin said, not all header pins can be used as GPIO. And some of the possible GPIO pins are used by the system (HDMI, EMMC2, I2C2, MCASP0 on BBB). About 30 pins are free. The way to configure them depends on the programing environment you intend to use (C, Cloud9, FreeBASIC, …). Specify the environment if you want concrete tips.

BTW: What do you mean by ‘I need to control 6 motors’? Is it on / off, direction, speed / angle position, …?

As I said I need to control my 6 motors with H bridges. For it I use 12 GPIOs as outputs for the H bridges and 6 GPIOs as inputs to detect with encoders when my motors take a round.
My BBB is on Angstrom and I program in C.

In that case it’s best to use libpruio. You can configure the pins (getting an error message when locked by the system) and control them (input and output) in an easy and fast manner. See stepper.c source code as an example.