fixes #93

API/Hardware_API.md

@@ -68,6 +68,61 @@ If you're newer to hardware and these functions look like alphabet soup to you,
 
 By default, all of the pins are pulled high if not specifically set.
 
+### Pullup and Pulldown pins
+
+Pins 2-7 on both Ports are available for pullup and pulldown.
+
+The basic function of a pull-up resistor is to insure that given no other input, a circuit assumes a default value. The 'pullup' mode pulls the line high and the 'pulldown' mode pulls it low.
+
+### Usage
+```js
+// Invoke this method to set the pull mode. pullType can be - pullup, pulldown or none.
+pin.pull(pullType, callback);
+```
+
+Example of the `pin.pull(mode)` command using a pushbutton. The code example given below turns on the Blue LED of the Tessel module when the pushbutton is pressed and turns off the Blue LED when the pushbutton is released.
+
+```js
+var tessel= require('tessel'); // Import Tessel
+
+var pin = tessel.port.A.pin[2]; // Select pin 2 on port A
+
+var pullType = "pullup"; // Set the mode of `pin.pull to pullup`
+
+var led = tessel.led[3]; // Blue LED of Tessel
+
+pin.pull(pullType,(error, buffer) => { // Pin 2 pulled high
+
+  if (error){
+    throw error;
+  }
+});
+
+setInterval({
+  pin.read(function(error, number){
+
+      if (error) {
+        throw error;
+      }
+
+      // Pin 2 reads high when the pushbutton is not pressed since it is pulled up
+      console.log(number);
+      if (number == 1){
+        led.off();
+      }
+
+      // Pin 2 reads low when the pushbutton is pressed since its connection with ground gets complete
+      else{
+        led.on();
+      }
+
+  });
+
+}, 500);
+```
+
+
+
 ### Digital pins
 
 A digital pin is either high (on/3.3V) or low (off/0V). Any pin on both ports A and B, other than 3.3V and GND, can be used be used as a digital pin. All pins are pulled high to 3.3V by default.

Tutorials/pinpull.md

@@ -0,0 +1,49 @@
+# Pull- Pins
+
+Suppose a pin is configured as an input. If nothing is connected to the pin and the program tries to read the state of the pin, it would be in a 'floating' state i.e an unknown state. To prevent this, a pull-up or a pull-down state is defined. They are often used in the case of Buttons and Switches.
+
+Pins 2-7 on both the Ports are available for interrupts.
+
+Take a look at the following circuit. The code example given below turns on the Blue LED of the Tessel module when the pushbutton is pressed and turns off the Blue LED when the pushbutton is released.
+
+![Pin-Pull using Push buttons](http://i.imgur.com/OYJZ8Dp.jpg)
+
+```js
+var tessel= require('tessel'); // Import Tessel
+
+var pin = tessel.port.A.pin[2]; // Select pin 2 on port A
+
+var pullType = "pullup"; // Set the mode of `pin.pull to pullup`
+
+var led = tessel.led[3]; // Blue LED of Tessel
+
+pin.pull(pullType,(error, buffer) => { // Pin 2 pulled high
+
+  if (error){
+    throw error;
+  }
+});
+
+setInterval({
+  pin.read(function(error, number){
+
+      if (error) {
+        throw error;
+      }
+
+      // Pin 2 reads high when the pushbutton is not pressed since it is pulled up
+      console.log(number);
+      if (number == 1){
+        led.off();
+      }
+
+      // Pin 2 reads low when the pushbutton is pressed since its connection with ground gets complete
+      else{
+        led.on();
+      }
+
+  });
+
+}, 500);
+```
+[More Information on Pull-up pins and resistors](https://learn.sparkfun.com/tutorials/pull-up-resistors)