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DHCP Client with Portenta H7 Breakout Board

JE
jeremybobbin
@jeremybobbin·Apr 11, 2026· 2 min read
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DHCP Client with Portenta H7 Breakout Board

premise

I wanted to make a simple, small device, with a single ethernet port just to acquire an IP address & display it on a small screen. This would serve as an easy-to-use network-debugging device & teaching tool.

I had thought the Portenta Breakout board with the Portenta H7 might work, considering the ethernet port.

ethernet

This is the segment I used to initialize the ethernet device & acquire an IP address via DHCP:

#include <SPI.h>
#include <Ethernet.h>

// Unique MAC address for your device
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

void setup() {
  Serial.begin(9600);

  // Attempt to get an IP address via DHCP
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");

    // Handle failure (e.g., stop execution or try static IP)
    while (1);
  }

  // Print the assigned IP address
  Serial.print("My IP address: ");
  Serial.println(Ethernet.localIP());
}

void loop() {
  // Maintain the DHCP lease (essential for long-running projects)
  Ethernet.maintain();

  delay(1000);
  Serial.print(".");
}

It worked the first try, fortunately.

link-light
new-ip

display

I tried to connect my LCD display to the display pins.

display

Since I had the display's "Reset" pin to the breakout-board's "D2N" pin, I tried compiling the following line

LiquidCrystal lcd(D2N, 0, 0, 0, 0, 0);

And I saw the following compilation error:

error: 'D2N' was not declared in this scope

D2N is not defined. Why would it be labeled that? Maybe it's defined in some library somewhere...

arduino-cli lib search portenta\ breakout

I installed the "Arduino_PortentaBreakout" library, however, I still saw the same message:

error: 'D2N' was not declared in this scope

What's the point of the library? I look at the header file, and see the following segment:

    ...
    DISPLAY_D3P = -1,
    DISPLAY_D3N = -1,
    DISPLAY_D2P = -1,
    DISPLAY_D2N = -1,
    DISPLAY_D1P = -1,
    DISPLAY_D1N = -1,
    DISPLAY_D0P = -1,
    DISPLAY_D0N = -1,
    ...

Not so useful... I tried using the DISPLAY_D2N variable:

LiquidCrystal lcd(DISPLAY_D2N, 0, 0, 0, 0, 0);

And saw:

error: 'DISPLAY_D2N' was not declared in this scope

Tracing the connections from the board to the jumpers, it looks like the display pins are pins 2, 4, 6, 8, 10, 12, 14 & 16 on J1 here:

pins

If anyone knows how those pins are defined in Arduino SDK, please let me know!

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JE
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