How to: Pin-outs

This article covers how to read the pinout section of any standard datasheet for a device, starting with the basics.

Before we get to any pins, however, we’re going to start with basic electronic terms. Voltage is actually a circuits potential difference between one end of a circuit element and another. If a battery has 0V connected to one end, and from the other end 9V is flowing from it, most would recognize this to be a 9 volt battery. However, if that same battery has 18V connected to one end and the other has 27V flowing from it, is it still a 9 volt battery? Of course! Because there is 9 volts of potential difference from one end to the other. Therefore, ‘ground’ is the minimum reference point for which the rest of the voltages are measured (in our second example, this would be 18V). Now that we’ve determined that ground is a reference point and not a fixed value of zero, we may continue.

On any given device designed to be interfaced with, there are open ‘pins.’ Oftentimes, these pins are grouped into standardized connectors- you’re probably familiar with USB. These standard connectors are comprised of 4 pins:

  • GND: Ground, the reference point upon which the connection’s voltage is measured.
  • D+ is unidirectional serial data transfer one way
    • Serial is sequencial binary bit transfer, for which a high voltage is a 1 and a low voltage is a 0
  • D- is unidirectional serial data transfer the other way
  • VCC: The positive terminal, which electrons from the ground source flow towards.

    usb_figure.png

Figure 1: Image via CodingRush

Now, for actually reading a datasheet! To find the pinout section of your datasheet, look for a ‘PINOUT’ or ‘INPUT/OUTPUT TERMINALS’ section of the datasheet. If you can’t find it through this, look for a large table with numbers along the side. Typical columns you would find on a pinout table are as follows:

  • The first column is usually just the actual pin numbers, read counterclockwise starting at the first pin to the left of a small indent in the chip. Innately, these have no importance other than objective identification of which pin is which.
  • The next column is generally the symbol applied to each pin number. With regards to our USB example, pin 4 is dubbed the symbol GND, pin 3 is D+, pin 2 is D-, and pin 1 is VCC, as shown in the image above.
  • After this column generally comes the classification of the pin, and special attributes of that pin, or a more descriptive column describing the function of the pin. 
    • Pins involved in powering the device are usually entitled the letter ‘P’: in this case, the power pins are GND and VCC. 
    • Pins designated to receiving data are termed with an ‘I’ for ‘input’: in the case of a standard USB cable, this would be the D- pin.
    • If you haven’t guessed it by now, the remaining pin classification is tagged as ‘O’ for output. This is the D+ pin

Here is an example pinout from a typical display datasheet. As you can see, the pin number and symbol columns are present, along with a function column describing the general purpose of each pin. VCC and VDD are for all intents and purposes the same; VCC is used when dealing with bipolar junction transistors, and VDD is used when dealing with field effect transistors. Regardless, it means ‘power’.

Sample Pinout Diagram

Most pinouts will include at least this much data on their tables, so next time you’re reading a data sheet check the pinout and see if you learned something today. Enjoy!

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