Two intelligent nodes are provided with the capability of negotiating a protocol between them so that if the intelligent nodes operate at two different protocols then they can select a protocol appropriate for their communication. The circuit further includes a pull-up current source selectively coupled to the first input of the second amplifier, and a pull-down current source selectively coupled to the first input of the second amplifier. The microprocessor comprises a central processing unit and a memory controller with a re-addressing device. A system for performing beating heart coronary artery bypass grafting includes a sternal retractor, organ manipulator and stabilizer.