Continued from [iPhone 5 Teardown (3)] All Components Slimmed Down
One of the major features of the iPhone 5 is the replacement of the 30-pin connector used in the previous models of the iPhone with the small "Lighting Connector." While the 30-pin connector includes pins for analog signals, Apple Inc said that the Lighting Connector "is completely digital and uses eight signals."
Also, the connector is "reversible," enabling the user to insert it to a port without paying attention to its orientation. While the connector has eight pins on each side, the receptacle of the iPhone 5 has pins only on one side. In other words, only one side of the connector is used for connection.
The change of the connector means that it becomes impossible to directly connect existing peripheral devices. And it causes negative impacts on manufacturers of those devices. Though Apple offers an adaptor that enables to use the Lighting Connector to connect peripheral devices designed for the 30-pin connector, peripheral device makers have to newly develop devices for the new connector.
So, there must be a compelling reason to change the connector. We started to analyze the Lighting Connector with help from an engineer who was well-versed in interfaces.
The iPhone 5 comes with a cable whose one end is a USB connector so that it can be connected to a personal computer by using the Lighting Connector. First, we checked which pin of the Lighting Connector is electrically connected to which pin of the USB connector.
A a result, we found a curious fact. The locations of USB's signals lines were different depending on the orientation of the Lighting Connector. Let's number the pins of the connector from 1 to 8 from the right end. We defined one side as the "top side." The pins on this side functioned as "GND (1), D+ (2), D- (3) and VBUS (4)."
However, the pins on the other side (Let's call it "bottom side") functioned as "GND (1), VBUS (4), D- (6) and D+(7). Though the locations of power supply lines (GND and VBUS) were the same, the locations of the signal lines (D+ and D-) were different.
The VBUS of the USB connector was not electrically connected to the Lighting Connector at first. But, when electricity is supplied to the USB side, an electrical potential appeared at the number 4 pin of the Lighting Connector. So, we estimated it to be VBUS.
At first, we expected that the pins on the two sides were connected so that they were point-symmetric. If so, the functions of the pins would be the same regardless of which side is used. When we examined which pin on the top side was connected to which pin on the bottom side. The number 1 and number 4 pins on the two sides (power supply lines for USB) were respectively (and diagonally) connected inside so that they became point-symmetric.
However, some of the pins were linearly connected. They were "the number 2 pin on the top side/the number 7 pin on the bottom side," "the number 3 pin on the top side/the number 6 pin on the bottom side," "the number 6 pin on the top side/the number 3 pin on the bottom side" and "the number 7 pin on the top side/the number 2 pin on the bottom side." Among them, the "the number 2 pin on the top side/the number 7 pin on the bottom side" functioned as D+ of USB, and "the number 3 pin on the top side/the number 6 pin on the bottom side" functioned as D- of USB.
Guessing the reason why those pins are connected in such a way inside the connector, the engineer said, "If the signal lines crossed one another, signals would be disturbed." It seemed that the iPhone 5, in some way, determines whether the "number 2/number 3" or "number 6/number 7" is used as USB signal lines.
If our guess is right, that means four pins ("the number 6 pin on the top side/the number 3 pin on the bottom side," "the number 7 pin on the top side/the number 2 pin on the bottom side," "the number 5 pin on either of the two sides" and "the number 8 pin on either of the two sides") are not used for USB connection.
According to a report titled "iPhone 5 costs up 28.7% from 4S; Lightning suppliers Cheng Uei & Hon Hai to benefit most," which was made by Taiwan-based KGI Securities, the Lighting Connector is provided by Taiwan-based Cheng Uei Precision Industry Co Ltd (Foxlink) and Taiwan-based Hon Hai Precision Industry Co Ltd. The report estimates that four pins of the Lighting Connector are used for transmitting signals, two for recognizing devices and two for supplying power.
Considering this estimate, it can be deduced that "the number 6 pin on the top side/the number 3 pin on the bottom side" and "the number 7 pin on the top side/the number 2 pin on the bottom side" are also signal lines and that the number 5 and 8 pins are used for recognizing devices. In other words, the Lighting Connector probably has two signal line systems, and only one of the two is used for USB (2.0) communication.
As mentioned earlier, connectors cannot be easily changed. So, it is quite likely that Apple offers an extra signal line system for future expansion.
"It might be possible to realize the high-speed data transmission of USB 3.0 by using the two signal line systems though it does not conform to USB 3.0 specifications and, thus, cannot be called USB 3.0," one of us said.
"The name 'Lightning' is suggestive," another said. "Apple used the name that can be associated with Thunderbolt on purpose. So, the iPhone 5 might support Thunderbolt in the future."
Those are just our guesses. But, the happiest moment for us is when we are thinking about those things. We will continue to analyze the Lightning Connector. And, when we find a new fact, we will report it.