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Phase Modulation uisng Parallel Port of AD9914

Question asked by volkanoznazli on Jun 19, 2017
Latest reply on Jun 21, 2017 by KennyG

Hello,

I want to use the parallel port of the AD9914 for making 8-bit phase modulation at 312.5MHz. My clock frequency is 3GHz. I intend to make use of only the bits [P7:P0] of the parallel port. All the other pins are externally grounded. I am using the programmable modulus mode to set the frequency. Next, I send amplitude information through the parallel port and then make the phase modulation.

 

Below is the flow in my code:

  1. Send a master reset to the part
  2. Set function pins to F[3:0]=0001 for serial programming
  3. CFR4: 0x01052120 (DAC calibration)
  4. Send IOUPDATE
  5. Wait 10msec
  6. CFR4: 0x00052120
  7. Send IOUPDATE
  8. CFR1: 0x00010300 (OSK enabled)
  9. CFR2: 0x00498900 (Parallel port enabled, digital ramp enabled, programmable modulus enabled, matched latency enabled)
  10. CFR1: 0x00010300 (OSK enabled)
  11. Digital ramp lower limit register: 0x1AAAAAAA (Programmable modulus 312.5MHz)
  12. Digital ramp upper limit register: 0x00000030 (Programmable modulus 312.5MHz)
  13. Rising digital ramp step size register: 0x00000020 (Programmable modulus 312.5MHz)
  14. Send IOUPDATE
  15. Set function pins to F[3:0]=0110; [P7:P0] = AMP[15:8] (Set amplitude using parallel port)
  16. Set [P7:P0] = 0xFF (Set amplitude using parallel port)
  17. Set function pins to F[3:0]=0111; [P7:P0] = POW[15:8] (Set phase using parallel port)
  18. From this point on, successive phase words are sent to make phase modulatio

 

Steps 1 to 16 work with no problem at all. I observe that the programmable modulus works nicely and I can set the frequency to the desired value.

 

My problem is that sometimes, during the transition from step 16 to 17, the amplitude is changed or completely lost as the function pins are changed from 0110 to 0111. This occurs for about 5% different runs. Do you have any idea of the cause of the problem?

 

I observe that I cannot observe any signal if I do not set the amplitude from parallel port and the problem is happening during transition of function pins. Is there any way of setting the amplitude other than the parallel port provided that the OSK is enabled?

 

Kind regards,

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