Patent ID: 7584384
Filing Date: 2009-09-01
Classification: G01R

Abstract:
1. A method of allowing a test mode of operation and a functional mode of operation of an electronic device wherein the device includes a number of inputs and outputs, test circuitry for carrying out the test mode of operation, functional circuitry for carrying out the functional mode of operation, monitor circuitry for detecting predetermined combinations of input signal states, power sense circuitry for detecting when power to the device is stable, timer circuitry for allowing a delay function, control circuitry for switching between the two modes of operation and multiplexer and driver circuitry including output drivers for selectively applying the outputs of either the test circuitry or the functional circuitry to a set of output terminals, the method comprising the following steps of operation: (a) directly after power up of the device, waiting until power to the device becomes stable, (b) at the completion of step (a), activating the test mode of operation during which the outputs of the device are controlled by the test circuitry and during which the functional circuitry operates normally in all respects in responding to input stimulus, but not in controlling the outputs of the device, (c) activating the delay function during which the test mode cannot be deactivated, (d) at the completion of the delay function of step (c), monitoring the inputs of the device until one of a number of specified conditions is detected and (e) when one of the number of specified conditions is detected in step (d), deactivating the test mode of operation and activating the functional mode of operation after which activation the outputs of the device are controlled by the functional circuitry and wherein at least one of the number of specified conditions is defined by a combination of input signals which cause the state of at least one part of the functional circuitry of the device to become a known state and wherein at least one of the number of specified conditions corresponds to a command which causes data to be written into the functional circuitry of the electronic device.