How to Detect That the Crystal is Working Correctly on the ADV7182/ADV728x

Document created by Rob.Analog Employee on Nov 29, 2013Last modified by Rob.Analog Employee on Nov 29, 2013
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This FAQ applies to the ADV7182, ADV7280, ADV7280-M, ADV7281, ADV7281-M, ADV7281-MA, ADV7282 and ADV7282-M.

 

Even if the external 28.63636 MHz crystal is damaged and does not oscillate:

  • I2C communication with the ADV7182/ADV728x will still work correctly.
  • It is possible to program the ADV7182/ADV728x normally will ADI scripts.
  • The ADV7182/ADV728x may even be able to partially lock to the incoming analog video source ( the IN_LOCK bit may be set).

 

However if the external 28.63636 MHz crystal is damaged and does not oscillate:

  • The ADV7182/ADV728x will not be able to output digital video correctly.
  • The INTRQ pin will not operate.
  • Unless a 28.63636 MHz crystal with a +/-50ppm accuracy is used, then the ADV7182/ADV728x will not be able to lock to the color sub-carrier frequency burst of incoming analog video (the FSC_LOCK bit will be low) . 

 

The fact that the INTRQ pin does not operate without a proper clock input, can be used to test if the crystal has become damaged. The attached script programs the ADV7182/ADV728x to drive the INTRQ pin low. If the crystal is working properly then the INTRQ pin will drive low. If the crystal is not present or damaged then the INTRQ pin will remain high (assuming a pull-up resistor to DVDDIO is present on the INTRQ output line).

 

The fact the FSC_LOCK bit will be low unless a crystal with the +/- 50ppm accuracy is used, can be used to test if the crystal is of the correct accuracy.

 

Note these tests can be carried out on ADV7182/ADV728x evaluation boards. Writing 0x04 to register 0x13 will cause the crystal to stop oscillating. See this post for more details. http://ez.analog.com/message/80298#80298

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