Abstract:
Testing an oscillator and other electronic devices on a circuit board. One method of the present invention comprises powering the oscillator. Providing test instructions to a microprocessor on the circuit board to place the microprocessor in a test mode. Receiving a clock signal from the oscillator at a multiplexer in a field programmable gate array. Receiving operating instructions at the multiplexer from the microprocessor. Multiplexing the clock signal to an external access port with the multiplexer in response to the operating instructions and measuring the frequency of the clock signal at the external access port.

Description:
TECHNICAL FIELD 
   The present invention relates generally to the field of electronic module testing and in particular a device for testing an oscillator and other electronic devices in a clock signal path on a circuit board. 
   BACKGROUND 
   A typical method of testing electronic devices coupled to an electronic module or circuit board is with the use of a test fixture. The test fixture typically has a bed of nails (spring probes) upon which the circuit board is mounted for testing. The spring probes make electrical contact with test points (access pins or ports) on the circuit board. In operation, the test fixture applies select signals to a select test point on the circuit board and monitors a response to the select signals at another select test point of the circuit board. Approximately 80 to 90 percent of the electronic devices on the circuit board can be tested with a typical test fixture. 
   The testing of a clock (or oscillator) on a circuit board is typically done by applying power to a select test point that is electrically coupled to the oscillator and taking a frequency measurement at another test point that is coupled to an output of the oscillator. If the frequency measured is a frequency that is expected, the oscillator is verified as working. However, if the measured frequency is not what is expected, the oscillator is not working properly. 
   Test fixtures are very expensive to purchase. Moreover, economically it is difficult to justify purchasing a test fixture if the volume of circuit boards produce is relatively low. In addition, the cost is doubled if the manufacture of the circuit boards takes place in two different locations and the testing needs to take place at both locations. It is desired in the art to have an efficient, non-expensive method of testing an oscillator on a circuit board. 
   For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved method of testing an oscillator on a circuit board. 
   SUMMARY 
   The above-mentioned problems as well as other problems are addressed by embodiments of the present invention and will be understood by reading and studying the following description. 
   In one embodiment, a method of testing an oscillator on a circuit board is disclosed. The method comprises powering the oscillator. Providing test instructions to a microprocessor on the circuit board to place the microprocessor in a test mode. Receiving a clock signal from the oscillator at a multiplexer in a field programmable gate array. Receiving operating instructions at the multiplexer from the microprocessor. Multiplexing the clock signal to an external access port with the multiplexer in response to the operating instructions and measuring the frequency of the clock signal at the external access port. 
   In another embodiment, a method for testing a signal generator for a circuit on a circuit board is disclosed. The method comprises powering the signal generator. Initiating a test mode for the circuit and in the test mode, selectively passing a signal from the signal generator to a port of the circuit for testing the signal form the signal generator. 
   In yet another embodiment, a method of testing electronic devices on a circuit board with a clock signal. The method comprises coupling a clock signal to a microprocessor. Coupling a test signal to the microprocessor. Passing operation instructions and the clock signal to a multiplexer in response to the test signal. Multiplexing the clock signal through the multiplexer to an external access port in response to the operation instructions and measuring the frequency of the clock signal at the external access port. 
   In further another embodiment, a tester for testing an oscillator on a circuit board is disclosed. The tester comprises a tester function that is adapted to transmit a test signal containing test instructions to a microprocessor on the circuit board, wherein the test instructions instruct the microprocessor to pass a clock signal formed by the oscillator to a multiplexer and to further instruct the multiplexer to multiplex the clock signal to an external access port. 
   In further yet another embodiment, a circuit board testing system is disclosed. The testing system comprises an external tester, a circuit board and a measuring device. The external tester is adapted to generate test instructions. The circuit board comprises a microprocessor, an oscillator, a field programmable array (FPGA) and a multiplexer. The microprocessor is selectively coupled to receive the test instructions from the external tester, wherein the microprocessor goes into a test mode upon receiving the test instructions from the external tester. The oscillator provides a clock signal. The field FPGA provides operational functions of the circuit board. The multiplexer is contained in the FPGA. The multiplexer is coupled to receive the clock signal as well as operational instructions from the microprocessor when the microprocessor is in the test mode. The multiplexer multiplexes the clock signal to an external access port in response to receiving the operational instructions from the microprocessor. The measuring device is selectively coupled to the external access port to measure the frequency of the clock signal at the external access port. If the frequency of the clock signal at the external access port matches an expected frequency the oscillator is verified as working properly. 
   In still another embodiment, an electronic module with testing functionality is disclosed. The electronic module comprises a microprocessor, a signal source, a functional circuit and a multiplexer. The microprocessor is adapted to receive test instructions from an external tester. The microprocessor goes into a test mode upon receiving the test instructions from the external tester. The signal source is coupled to the microprocessor to provide a signal. The functional circuit is operatively coupled to the microprocessor to provide operation functions of the electronic module in non-test modes. The multiplexer is contained in the functional circuit and is adapted to receive the signal from the microprocessor. The multiplexer is further coupled to receive operation instructions from the microprocessor when the microprocessor is in the test mode. Moreover, the multiplexer multiplexes the signal to an external access port in response to receiving the operational instructions from the microprocessor in test mode. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which: 
       FIG. 1A  is a block diagram of testing system according to one embodiment of the present invention; 
       FIG. 1B  is a block diagram of a testing system according another embodiment of the present invention; and 
       FIG. 2  is a flow chart illustrating the implementation of one embodiment of a method of the present invention. 
   

   In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the present invention. Reference characters denote like elements throughout Figures and text. 
   DETAILED DESCRIPTION 
   In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
   Embodiments of the present invention allows for the testing of an oscillator on a circuit board without the use of a test fixture. In particular, embodiments of the present invention test the oscillator (or generator), as well as other electronic devices of the circuit board, by passing a clock signal from the oscillator through the other electronic devices of the circuit board and then measuring the frequency of the clock signal at an already existing access point on the circuit board. The tests used in the embodiments of the present invention can occur even when the circuit board that contains the oscillator is mounted in its normal operational location. That is, testing of the oscillator using embodiments of the present invention does not require the attachment of the circuit board to a bed of nails in a test fixture. 
   Referring to  FIG. 1A , one embodiment of an oscillator testing system  100  of the present invention is illustrated. As illustrated, the oscillator testing system  100  includes a circuit board  101  and a tester  130 . In particular, in the embodiment of  FIG. 1 , generally only the electronic devices on the circuit board  101  that focus on this embodiment of present invention are illustrated. The electronic devices include an oscillator  102 , a microprocessor  104 , a random access memory (RAM)  106 , a system bus  107 , a field programmable array (FPGA)  108  (or application specific integrated circuit  108 ), a buffer  114 , an access port  116 , a universal asynchronous receiver/transmitter (UART)  118 , and a UART port  119 . The FPGA typically performs the functions of the circuit board  101  and is electrically coupled to an external port. The FPGA  108  includes logic circuit  112 . In particular, logic circuit  112  includes all of the circuits typically used in forming a FPGA  108 . In addition, the FPGA  108  is illustrated as including multiplexer (MUX)  110 . 
   In embodiments of the present invention, normal activation power is supplied to oscillator  102 . Oscillator  102  produces a clock signal used to clock the microprocessor  104  in response to the activation power. Tester  130  is coupled to the UART port  119  to supply test instructions to the microprocessor  104  via the UART  118 . In response to the instructions, the microprocessor  104  enters into a test mode and passes the clock signal through the system bus  107  to MUX  110  of the FPGA  108  along with instructions to MUX  110 . In response to the instructions, MUX  110  passes the clock signal to buffer  114 . Buffer  114  is used to change voltage levels. In particular, buffer  114  in this embodiment is an output buffer  114  that provides a passageway to access port  116 . Access port  116 , in one embodiment, is an existing input/output pin. In other embodiments, in which a passageway to an external port does not flow through a buffer, a buffer is not required. The frequency of the clock signal is measured at access port  116 . 
   The tester  130  of the embodiment of  FIG. 1A  includes a tester function  132  and a measuring device  134 . The tester function  132  provides a test signal, containing the test instructions, to the UART port  118 . The measuring device  134  is adapted to measure the frequency of a clock signal and, in this embodiment, is selectively coupled to measure the frequency of the clock signal  120  off access port  116 . In other embodiments a separate different tester is used to measure the frequency. In further embodiments the oscillator is coupled directly to a FPGA. In these embodiments, a clock signal passes directly from the oscillator to a multiplexer in the FPGA and then to an external port under the control of a microprocessor. An example of an embodiment in which the clock signal passes directly from the oscillator  102  to MUX  110  in the FPGA  108  is illustrated in FIG.  1 B. The testing system  150  of  FIG. 1B  is similar to the testing system  100  of  FIG. 1A  except, as illustrated, connection  170  connects the oscillator  102  to the system bus  107 . The system bus  107  is coupled to MUX  110  in the FPGA.  FIG. 1B  also illustrates, an embodiment where the measuring device  134  is in a different tester  160  than the tester  130  that contains the tester function  132 . 
   Referring to  FIG. 2 , flow chart  200  illustrates a method of use for one embodiment of the present invention. As flow chart  200  illustrates, the method starts by applying power to the oscillator  102  that supplies the clock signal to the microprocessor  104  ( 202 ). The tester applies test instructions to the UART  118  which are passed on to the microprocessor  104  ( 204 ). The test instructions direct the microprocessor  104  to enter into a test mode. Once in the test mode, the microprocessor  104  passes the clock signal from the oscillator  102  along with operation instructions to the MUX  110  in the FPGA  108  via the system bus  107  ( 206 ). In response to the operation instructions received, the MUX  110  multiplexes the clock signal to buffer  114  ( 208 ). The buffer  114  then passes the clock signal on to the access port  116  ( 212 ). The frequency of the clock signal is measured at access port  116  ( 216 ). If the frequency of the clock signal matches an expected frequency ( 218 ), the oscillator  102 , as well as other electronic devices in the clock signal path, are verified as working ( 222 ). If the frequency of the clock signal does not match an expected frequency ( 218 ), the oscillator  102  is not verified as working properly ( 220 ). 
   Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.