ADC32RF45EVM: Can't read back what was written to a register

Hi,

When the SPI GUI reads back all zeros for all of the paged ADC registers then that almost always means that the data converter is not getting the sample clock or it is not getting the SYSREF signal.  That is why the order of configuration needs to be to configure the clocking first and then configure the ADC.  If you are using the Quick Setup tab of the SPI GUI then the GUI will load the appropriate config file for the LMK04828 clock device first, then the LMX2582 clock synthesizer if it is chosen in the setup, and then the ADC.  If you are using the low level tab to load config files directly then they will need to be done in this order.   Be sure to set the jumper for internal or external clocking for EXT if you are supplying  clock to J5 and J7, otherwise set it to INT if you are choosing the clock as LMX2582 to the ADC.   If you are choosing to use the LMK04828 for clock to the ADC then you need to set the jumper to INT as well as move two AC coupling caps.   If using external clocking, you may need to start probing to check the clock amplitudes into the EVM and up to the ADC pins.

Also, make sure you have a 5V supply rated for about 3A or more for the EVM supply.  I have seen it happen that the inrush current at the time of ADC config would cause a brownout of the supply momentarily, after which the SPI registers would have lost the configuration that was just written. 

Regards,

Richard P.

Hi Richard,

I'm not sure why half of my post is missing but I am using an external clock, the jumper is in the external position, I'm using the quick setup tab, and I'm using a 5V 5A power supply.

I have verified that the sysref signal is not present by probing. I'm using a signal generator for the clock input. The frequency is set to 2.94912GHz and the amplitude is 1V (Max for signal generator).

Here are the steps I follow:
1. On the PLL1 tab of the LMK04828 tab, press the RESET button.
2. On the ADC32RFxx-EVM, press SW1 (ADC RESET) to provide a hardware reset to the ADC.
3. Click on the Quick Setup tab
4. Select the Nyquist Zone for the input. It will be 2nd Nyquist in this example setup (Fs = 2949.12M, Fin
= 1900M).
5. Select the Clock Source to ADC. In this example, External Clocking is selected
6. Select ADC32RF45 Mode. In this example, Bypass is chosen.
7. Select Resolution. In this example, 12 bit is selected.
8. Press PROGRAM EVM.

9. Once completed I verify that I can read the ADC by clicking on the Low Level View tab.
10. Scroll down to ADC32RFxx_DIGITAL
11. Read register 0x01

The result of this is that register 0x01 reads 0x00 when it should read 0x80.

What I don't understand is that this procedure should have initialized the system to generate a sysref. My only thought is that by clicking bypass on the Quick Setup tab, we completely bypass the clock generator chip all together and the clock generator chip never outputs a sysref.

Thanks,
Robert

Hi Richard,

Do you have any idea as to why the SYSREF signal isn't being generated? I double checked the clocks going into the LMK04828 and it is correct at 2.94912GHz. Going through the quick setup guide should have yielded a SYSREF but it doesn't.

Thanks,

Robert

Hi,

thank you for letting us know the resolution.  we will keep this in mind for future board revisions.

Regards,

Richard P.