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In this video, you'll learn how to configure the AFE74XX EVM to selectively switch between the three available RX NCOs using GPIO pins. For more details, visit ti.com/afe74xx. Let's take a closer look at the schematic to see how switching the receiver NCOs view GPIO works.

On page 4, the AFE74XX schematic, look for the GPIO pin bank labeled AFE control. Here, we find an array of GPIO pins all serving different functions. The pins responsible for dynamically selecting the active RX NCOs are seen here at GPIO pins 14, 17, 20, and 23. Each of these GPIO pins are low and grounded, and are high when pulled up to 1.8 volts. Pins RXFBNCO0 and RXFBNCO1 determine which NCOs selective for ADCA and ADCB.

This is a table that displays which NCO will be active given a combination of the two pins. As seen in the table, when pins RXFBNCO0 and RXFBNCO1 are both low, NCO0 is selected for both ADCA and ADCB. When pin RXFBNCO0 is high, and pin RXFBNCO1 is low, NCO1 is active. When pin RXFBNCO1 is high, and pin RXFBNCO0 is low, NCO2 is active. Pins RXFBNCO2 and RXFBNCO3 both determine which NCO is active in ADCC and ADCD.

Now, I'll show you an example of how to use GPIO pins RXFBNCO0 and RXFBNCO1 to dynamically hop between three single bend NCOs and ADCA. Here, you can see I have the AFE74XX EVM connected to the TSW14J57 EVM. For more detail on how to set up the hardware, check out the video in this series called "Setting Up The Hardware."

There is an input signal source generating the input signal through a bandpass filter, and is connected to AN1, which is the ADCA input. The input signal source is set to output 1.9 gigahertz at minus 11 DBM. The 10 megahertz reference signal from the back of the signal generator is connected to LMK Clock In for coherent sampling. I will remove the jumpers located at GPIO pins 14 and 17. These pins are RXFBNCO0 and RXFBNCO1, responsible for NCO selection for ADCA and B as mentioned earlier.

Remove the jumper JP3 titled RXFBNCO. This jumper outputs logic high voltage of 1.8 volts on one of its pins. Connect the female to female jumper cable to the pin that outputs 1.8 volts. We will use this to turn on either RXFBNCO0 or RXFBNCO1.

Before bringing up the AFE74XX EVM in mode 4, let's configure the RX NCOs on the AFE74XX EVM using the AFE74XX GUI. Launch the AFE74XX GUI as administrator. Select the appropriate settings to bring up the AFE74XX in mode 4. For more detail on these settings, reference the video in this series titled "Bringing Up The DAC In The AFE74XX."

After selecting mode 4 in the AFE mode selection tab, switch to the Advanced panel. Now, I'm going to program the NCOs and the ADCa. For more detail on this section, reference the video in this series titled "Configuring The RX NCOs."

I will set NCO0 1,600 megahertz, NCO1 to 1,700 megahertz, and NCO2 to 1,800 megahertz. I will set RX ID to RX0 since I'm programming the NCOs in ADCA only. I will set the RX NCO IDs to 0, 1, and 2 because these are the NCOs that I'm programming. Then I will click RX NCO Update.

Then in the section that says Dynamic Switch, I will click the dropdown under RX_FBRX and select On. In the dropdown box titled RX/FBNCO, I will select NCO Selection by RX FB NCO. After this, I will navigate back to the Quick Start page and select Set Mode. This programs the onship LMK. Then I'll click Run Complete Startup to program the AFE74XX.

Once it's finished programming, open HSDC Pro and connect the board. When prompted to upload the firmware, press OK. Then in the ADC tab, select AFE74XX_RX_Mode4. Under ADC Output Data Rate, enter 737.28 megahertz. Navigate back to the Advanced panel in the AFE74XX GUI and press the ADC button to reinitialize JESD handshaking.

Navigate back to HSDC Pro and press Capture. Right now, both RXFBNCO0 and RXFBNCO1 GPIO pins are low, so we should expect for NCO0, which is set to 1,6000 megahertz, to be active. NCO0 should down convert the 1,900 megahertz input signal to 300 megahertz before capturing. The down converted signal is located at 300 megahertz as expected.

Now, I will pull the RXFBNCO0 pin high while the RXFBNCO1 pin is still low. This should enable NCO1, which is set to 1,700 megahertz. We should expect the captured signal to be located at 200 megahertz. When pressing Capture in HSDC Pro, we verify that NCO1 is, indeed, enabled.

Now, I will pull RXFBNCO1 high while RXFBNCO0 is still low. This should enable NCO2, which is set to 1800 megahertz. We should expect the captured signal to be located at 100 megahertz. When pressing Capture in HSDC Pro, we verify that NCO2 is enabled.

The time it takes to switch from one NCO to another via GPIO is approximately 250 nanoseconds. To learn more about the AFE74XX and how it can speed up your design process, visit ti.com/afe74xx, and make sure to check out the other videos in this series. Thanks for watching.