Method and apparatus for controlling operating modes of an electronic device

A method of operating an electronic device, the electronic device having a number of inputs and outputs including a number of digital functional inputs and outputs, a test mode of operation and a functional mode of operation, wherein circuitry for the test mode of operation includes combinational continuity test circuitry for externally conducting continuity tests of connections between connections of the digital functional inputs and digital functional outputs of the electronic device and input and output connections of other electronic devices to which the electronic device connects and wherein the continuity test circuitry within the electronic device operatively coupling at least a majority of the digital functional inputs to digital functional outputs of the electronic device is combinational logic, the electronic device further including functional circuitry for carrying out the functional mode of operation, control circuitry for switching between the test and functional modes of operation and output circuitry for selectively applying outputs of the test circuitry and the functional circuitry to digital functional outputs of the electronic device, the method comprising the steps of:

• (a) providing stimulus at one or more device inputs causing detecting and decoding circuitry coupled to one or more device inputs to select between the test mode of operation and the functional mode of operation;
• (b) providing stimulus at a plurality of the digital functional inputs of the electronic device causing other detecting and decoding circuitry coupled to those digital functional inputs of the electronic device to detect and decode as one or more commands for conducting other tests, one or more combinations which have been categorized as superfluous to conducting practical continuity testing of operatively coupled input signals applied concurrently to the digital functional inputs by the other electronic devices;
• (c) activating other testing circuitry coupled to the detecting and decoding circuitry and active during the test mode of operation to carry out the other tests in response to the commands detected and decoded;
• and,
• (d) activating circuitry coupled to the other detecting and decoding circuitry for selecting outputs of the other testing circuitry as outputs of the test circuitry when the other tests are active and in the absence of the other tests being active, selecting outputs of the combinational continuity testing circuitry for conducting continuity testing.

Apparatus included in an electronic device, the electronic device having a number of inputs and outputs including a number of digital functional inputs and outputs, a test mode of operation and a functional mode of operation, wherein circuitry for the test mode of operation includes combinational continuity test circuitry for externally conducting continuity tests of connections between connections of the digital functional inputs and digital functional outputs of the electronic device and input and output connections of other electronic devices to which the electronic device connects and wherein the continuity testing circuitry within the electronic device operatively coupling at least a majority of the digital functional inputs to digital functional outputs of the electronic device is combinational logic, the electronic device further including functional circuitry for carrying out the functional mode of operation, control circuitry for switching between the test and functional modes of operation and output circuitry for selectively applying outputs of the test circuitry and the functional circuitry to the digital functional outputs of the electronic device, the apparatus comprising:

• (a) detecting and decoding circuitry coupled to one or more device inputs to select between the test mode of operation and the functional mode of operation;
• (b) other detecting and decoding circuitry coupled to the digital functional inputs of the electronic device for detecting and decoding as one or more commands for conducting other tests, one or more combinations which have been categorized as superfluous to conducting practical continuity testing of operatively coupled input signals applied concurrently to the digital functional inputs by the other electronic devices;
• (c) other testing circuitry coupled to the detecting and decoding circuitry and active during the test mode of operation to carry out the other tests in response to the commands detected and decoded;
• and,
• (d) circuitry coupled to the other detecting and decoding circuitry for selecting outputs of the other testing circuitry as outputs of the test circuitry when the other tests are active and in the absence of the other tests being active, the circuitry selecting outputs of the combinational continuity testing circuitry for conducting continuity testing.

Apparatus included in an electronic device conforming to a form of the Proposed IEEE P1581 Architecture that supports only continuity testing, the apparatus comprising:

• (a) detecting and decoding circuitry coupled to digital functional input connections of the electronic device for detecting and decoding one or more of the combinations of operatively coupled input signals applied to the digital functional inputs of the electronic device, the one or more combinations being categorized as superfluous to conducting continuity testing applied to the device digital functional input connections as one or more commands for performing other tests;
• (b) other testing circuitry coupled to the detecting and decoding circuitry and active during the test mode of operation to carry out the other tests in response to the combinations of operatively coupled input signals detected and decoded as commands by the detecting and decoding circuitry;
• and,
• (c) circuitry responsive to signals from the detecting and decoding circuitry to selectively apply outputs of the continuity test circuitry or the other test circuitry to the outputs of the device during test mode.