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Table of Contents
On this page we'll describe the 10 “DIO” Digital I/O connections on the RoboRIO.
Introduction
By “digital” or “binary” we mean that each connector can convey a piece of information that is in one of two conditions. There are several ways of saying this:
- on / off
- one / zero
- Positive voltage / zero volts
When acting as an input, the RoboRIO interprets any voltage between 0 and 0.8v
By “IO” we mean that the direction can be either:
- Input: from an external switch or sensor to the RoboRIO
- Output: from the RoboRIO to an external light or other device
The direction is controlled by the software that runs on the roborio (see below).
Each “DIO” consists of a header with 3 pins. Typically, we connect a 3-wire “PWM” cable to each header.
- Ground (black)
- +5v power (red)
- Signal (white)
The interesting pin is the “signal” pin. When configured as an output, the signal pin is driven to 0 volts for a “zero”, and 3.3 volts for a “one”. More on outputs later.
When acting as an input, the RoboRIO interprets any voltage between 0 and 0.8v ad a “zero”, and a voltage between 2.0v and 5.5v as a “one.” A voltage in between those ranges results in either a zero or a one being delivered to the software program.
There is a “pullup” or “pulldown” resistor internal to the RoboRIO that helps ensure that the voltage on a disconnected DIO does not drift into that “unknown” region. For the ten basic DIOs on the RoboRIO, it is a pullup, so an unconnected DIO will be read by software as a “one”.
To cause a DIO to be read as “zero” by software, all we have to do is connect the signal pin to ground, for example with a switch.
[picture needed]
Software
Here's a Java code fragment:
package edu.wpi.first.wpilib.templates;
import edu.wpi.first.wpilib.DigitalInput;
import edu.wpi.first.wpilib.SimpleRobot;
import edu.wpi.first.wpilib.Timer;
public class RobotTemplate extends SimpleRobot {
DigitalInput mySwitch;
public void robotInit() {
mySwitch = new DigitalInput(1);
}
public void operatorControl() {
more code here
switch_now = mySwitch.get();
if(switch_now) {
do somthing if the switch is open (“one”);
} else {
do somthing else if the switch is closed (“zero”);
}
more code here
}
}
There's some more software discussion here: * https://wpilib.screenstepslive.com/s/3120/m/7912/l/599687-using-limit-switches-to-control-behavior
Conclusion
This discussion also applies to the 16 additional DIO pins located on the roborio expansion connector.