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I am making PCB with RP2040 and W5500. I am looking these schematics. first , second. In this designs,the first is using gnd and cgnd.The second is using agnd. I know the digital gnd is much more noiser that analog agnd. In real design (i couldn't do it yet) which one should I fallow ? For example I am using W5500 for http request. If I use gnd will it increase my wait time? I am wondering if I use agnd, can my http request faster? I wanted to ask because I have no experience with either.

My second question is when I looking for designs I saw cgnd is connecting to agnd's polygon. Why are we using cgnd then?

Can I use GND instead of CGND for this photo?

enter image description here

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The RP2040 chip itself doesn't have AGND. Some boards dedicate a quiet part of the PCB for a ground polygon that's dedicated to the ADC inputs, and call it AGND. The idea is that digital ground currents will not mix with analog ground currents on their way back to the RP2040. If you're not using the ADC inputs, you don't need to concern yourself with AGND.

Normal digital ground noise will make no difference to servicing HTTP requests.

A bad ground layout would simply degrade any analog circuits you have on your board.

A terrible ground layout could cause the chip to reset or otherwise glitch, I guess that could count as slowing down your HTTP request ;)

As long as you don't have noisy motor drivers or very sensitive analog parts in your design a simple ground plane should be just fine.

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  • \$\begingroup\$ Thank you, DamienD. This answers my questions. "As long as you don't have noisy motor drivers". I couldn't say it I didn't know motor driver can be problem. I will use D-808 Motor driver but I will use only signals pins. I will give power D-808 from another adapter ( Switch mode adapter.) Will it be a problem ? I am using hx711 IC too but It is working good with GND. \$\endgroup\$ Oct 26, 2021 at 10:31
  • \$\begingroup\$ I checked Sparkfun's hx711. They connected it GND too. \$\endgroup\$ Oct 26, 2021 at 10:37
  • \$\begingroup\$ You will be using the RP2040's single GND pad anyways. Grounding is a huge topic! But as a general rule make sure that the motor drivers have a direct path to the power connector and back, and keep the other chips away. \$\endgroup\$
    – DamienD
    Oct 26, 2021 at 11:10
  • \$\begingroup\$ Okay, thank you . \$\endgroup\$ Oct 26, 2021 at 11:14
  • \$\begingroup\$ In your case, do make sure that there is a shared ground between all your parts, as you have several supplies \$\endgroup\$
    – DamienD
    Oct 26, 2021 at 11:16

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