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The first version of Lucy's communication was created with a sixteen bit parallel databus via a special designed ISAbus card. But the length of the cable had to be limited in order not to induce too many communication errors. To overcome this restriction we implemented a serial communication based on USB 2.0. The bit rate of the 2.0 version is about 480 MBit per second which is high enough to assure a proper communicationspeed.
The hardware implementation of the protocal is achieved with the EZ-usb FX2 micro-controller. This controller is attached to the robot and connected with the other micro-controllers by a 16 bit parallel bus.
Each low-level micro-controller has a 16 bit dualported RAM unit which separates its own bus from the global parallel data bus. These RAM units assure that there will be always valid data ready to be tracked by the local control unit. Whenever the PC didn't manage to calculate new trajectory values in time, the local micro-controller will still have the old values stored in the dualported RAM unit.
Picture of USB microcontroller with electronics for the 16 bit parallel databus (Click picture to enlarge)>

Information about the microcontroller EZ-USB FX2 from Cypress Semiconductors

Vrije Universiteit Brussel,    Faculty of Applied Sciences,     Department of Mechanical Engineering
Pleinlaan 2,    1050 Brussels,    tel. 32-2-629.28.06,    fax 32-2-629.28.65
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