ONES AND ZEROS,HIGHS AND LOWS

As you should already know, a computer program manipulates data in the form of binary digits, 1s and 0s. This data may represent characters, times, temperatures, button pushes, alarm signals, screen pixels, the list is almost endless. But in the computer it's all 1s and 0s. When any computer, and in particular a microcontroller, interfaces with the real world as it must, there must be a translation between these 1s and 0s and external voltages on the device pins. It is enough now to know that externally a 1 will be represented to and from the uC by a high voltage (we'll talk later about how high is high) and a 0 will be represented by a low voltage (again, details will follow). Like every other rule there can be exceptions, but for now just remember 1=high, 0=low. We will try to use "1" and "0" when talking about logical states (the data in the program) and "high" and "low" when talking about signals external to the uC, but we may fuzz up that dividing line now and then.