Peter Teffer, http://www.peterteffer.com, recently contacted me asking for a small interview on the new Type-C USB connecter. I was happy to oblige and wrote the interview below. However, for some reason he did not use near as much of it as I thought he would. Don't know why, maybe he had different ideas that I did. No harm, I appreciate him contacting me and asking.
Peter:
Dear Mr Lunt,
I'm a journalist from The Netherlands writing a story about the new USB Type-C connector. The great advantage from a consumer point of view is that the new USB cable solves the 'upside down' problem - no longer will it matter what side is up when connecting the USB cable.
Since you know so much about the topic, I would like to interview you via e-mail. I have two questions.
Why was the USB cable designed in such a way that it could be connected only one direction, and why did it take so long before there was a solution for the "plug orientation/cable direction" problem?
Ben:
Hi Peter,
Thank you for contacting me and for the kind words. I would love to answer your questions.
I have answered both questions in one answer, so to speak, and have given more than you probably were expecting. You may take this as you wish, shortening or expanding as you see fit.
Please note that I have not seen the specifications for the new Type-C Connector and the information below is only my opinion of what could happen.
Thank you for your questions. As you can tell, I do enjoy the USB and am grateful for your request.
Thanks,
Ben
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I have been working with USB for about 15 years and have enjoyed the research and development I have made through those years. The most enjoyable result was the publication of "USB: The Universal Serial Bus".
As you might know, the original cables and up to the USB 2.0 specification, all had four wires, a Voltage/Current pair, and the Data pair. The Voltage/Current pair consisted of the positive and ground wires, while the Data pair consisted of a D+ and a D- pair, the communications pair.
The USB device this cable plugged in to, was wired so that it knew which pin was the positive, or Voltage/Current pin, and which pin was the grounding pin. If the connector was made so that the cable could be plugged in either way, these two pins might be switched.
If you imagine four connecting pins laid out in a horizontal row, the Voltage/Current and Grounding pair is the two pins on the outer edges, while the Data pair is the two pins in the middle. If the cable was plugged in upside down, each pair of pins would now be swapped.
To overcome this problem, the manufacturers could have included a small voltage rectifier (image shown to the right) and this would have fixed the issue with the Voltage/Current and Grounding pair. However, this would add a small cost to each device, another requirement to the specification, and other issues such as a possibility of voltage fluctuations due to various kinds of rectifiers available.
However, the real issue of an upside down insert would be the swapping of the two Data pins. The USB specification uses a resistor on one of the Data pins to indicate what speed the device is, Low or Full. If the device is a Full Speed device, it will have a 1.5k resistor from the Voltage/Current pin to the D+ pin, or for a Low Speed device, on the D- pin.
If these two Data pins are now reversed, the speed identification of the device is now reversed. Also, the micro-controller on the device has its two Data pins already hard coded. It would require a considerable amount of additional hardware to compensate for this.
I am sure that the USB-IF could have created an addition so that the device would have to compensate for the possible swapping of pins. However, in 1994, these micro-controllers and other chips were not as inexpensive as they are today. In my opinion, the USB-IF did not want to add unnecessary cost to the devices that would soon flood the market.
Now that there are so many devices that use USB and then so many more that use the connecting form of the USB for power; cell phones, tablets, etc., it has been a long time coming to have a reversible form of connection.
How many times have you been ready for bed, the lights out, and need to plug your phone in before you call it a day? If you can find the connecting slot on the device, which way is it facing, especially with the Type-B Micro connector?
As far as how the USB-IF will implement the design of the new Type-C Connector, I don't know yet. It has been rumored that it will be close to the Type-B Micro Connector.
This Type-B Micro Connector has an advantage that was given from the beginning...a fifth pin. This type of connector left an unused pin. Again, imagine a line of 5 pins in a row, Pin 1 on the left, and Pin 5 on the right. Again, the two outer pins are the Voltage/Current and Grounding pins. If these two were swapped, a simple, and a now very inexpensive voltage rectifier could be used.
Pin 2 is the D- pin and Pin 3 is the D+ with Pin 4 unused. If the connector was now plugged in upside down, Pin 3 would still be the D+ connector. However, now the D- connector is on Pin 4. Since Pin 4 was originally unused, what if Pin 2 and Pin 4 were always connected on the PCB? Now, you would only need to include a voltage rectifier on the new device and you could plug the cable either way.
However, you now need a different shape for the connector to indicate that this new device does have a voltage rectifier and Pins 2 and 4 connected.
One more thing to notice is that the USB 3.0+ Type-B Micro connector has these five pins as well as five more for the Super-speed connectors. Could these five pins also be "rectified", knowing that you only have to "rectify" four of them?
The above form of fixing the upside down issue is only my opinion. I don't have any information on the new Type-C Connector type yet, so it could be completely different...or maybe not. (smile)
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