add binary counter example

1_Basic_GPIO/digitalOut.md

@@ -224,3 +224,25 @@ Code to turn the fan on and off with a 2 second delay:
 }
 
 ```
+
+## Binary LED Counter
+
+This example uses 5 LEDS to visualize a 5 bit binary counter. Mask commands are used to set the LEDS simultaneously.
+
+```c
+int pinMask = 0b1111100000000000;
+int dirMask = 0b1111100000000000;
+int counter = 0;
+gpio_init_mask(pinMask);
+gpio_set_dir_masked(pinMask, dirMask);
+while (true)
+{
+    gpio_put_masked(pinMask, counter<<11);
+    counter++;
+    sleep_ms(500);
+}
+```
+
+`gpio_put_masked` has similar characteristics as other masked functions. This will set the output pins according to the second argument simultaneously, `counter<<11` in this case. Counter is left shifted by 11 bits to align with the mask.
+
+if counter is `11001`, `counter<<11` will be `1100100000000000`.