Electronic Design
Thunderbolt and Light Peak

Thunderbolt and Light Peak

Thunderbolt and Light Peak reminded me of the Clint Eastwood film Thunderbolt and Lightfoot. It is a yarn about bank robbers that like to blast open the safe using a 20mm cannon. In this case, however, Thunderbolt refers to the new high speed display and data connection from Intel and Apple. The Thunderbolt architecture (Fig. 1) combines two existing standards: PCI Express and DisplayPort. It could challenge USB 3.0 in many areas but it tends to be complementary because of its display capability that is secondary for USB. It competes against similar alternatives like Icron Technologies USB display solution Displaylink also provides display solutions based on USB (see Time for PC Modularity?).

Intel's Thunderbolt chip (Fig. 2) ties into a standard PCH (platform controller hub) via a PCI Express x4 connection(Fig. 3). The chip is essentially a DisplayPort controller with PCI Express switch and one of the switch connections goes to the connector. It is simple. It employs standards and it will be a game changer.

It is quite possible that Thunderbolt could push DisplayPort out of the way because of the PCI Express connection. DisplayPort alone has significant advantages including the ability to daisy chain up to 7 devices together. It can handle up to two high resolution DisplayPort v1.1 displays. The problem is that it lacks data transfer capabilities at the level of functionality that PCI Express provides. In theory, a USB 3.0 and DisplayPort combination could have been used but Thunderbolt can easily handle USB 3.0 by adding a PCI Express USB controller on any device. The reverse does not work very well.

Although Thunderbolt will handle optical cabling, hence the Light Peak code name, its first incarnations employ all copper connections. This is likely to be the normal connectivity mode since 3m Thunderbolt cables (Fig. 4) should handle most applications. The cables do provide up to 10W of power so many devices may not require additional power cables. Like USB, PCI Express and DisplayPort, Thunderbolt supports hot swapping.

The use of standard, bidirectional technologies allows peer-to-peer communication. Switches can provide different topologies including trees. The system also employs a time synchronization protocol that can synchronize devices to within 8ns. This may not be fast enough for some test and measurement systems but it is more than adequate for many. It is also ideal for many process control or robotic applications.

Thunberbolt that will start appearing on Apple's latest Mac laptops (Fig. 5). It will need to be matched with display technology but you can bet that is on the way already.

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