Patent ID: 6897678
Filing Date: 2005-05-24
Classification: G01R

Abstract:
1. A method for observing logic element signals in a programmable logic device having a plurality of logic elements, a plurality of logic element registers, each contained in a respective one of the logic elements and each having a logic element register output, logic element logic in each logic element that provides logic signals, a switching circuit associated with each logic element that has a logic element input connected to the logic element logic for receiving the logic signals, a scan chain input, and a switching circuit output for providing signals to the logic element register contained in that logic element, and a plurality of scan chain conductors each connecting the logic register output of a logic register in one of the logic elements to the scan chain input of the switching circuit associated with a successive one of the logic elements to form a continuous scan chain, the method comprising the steps of: configuring the switching circuits during normal operation to connect their logic element inputs to their outputs so that the logic signals are stored in the logic element registers; and configuring the switching circuits during register observation to connect their scan chain inputs to their outputs so that the logic signals stored in the registers may be scanned out of the registers through the continuous scan chain.