USB

  • usb
  • USB
  • USB Serial
  • iSerialNumber
  • COM

If the USB D+ pin on an ESP32 module is configured as input with pull-up, why can't an external 10K pull-down fully pull it to GND, and what should be noted?

IO20 is the USB D+ signal pin. In non-USB mode, this pin includes an internal weak pull-up resistor. Because the internal pull-up is much stronger than an external 10K pull-down, the pin voltage is held at a relatively high level by the divider effect instead of being pulled to GND. To resolve this, the internal pull-up must be forcibly disabled through the corresponding register.

// Include the header
#include "soc/usb_serial_jtag_reg.h"
// Clear the register bit to forcibly disable the internal weak pull-up on USB D+
REG_CLR_BIT(USB_SERIAL_JTAG_CONF0_REG, USB_SERIAL_JTAG_USB_PAD_ENABLE);
// Configure GPIO
...

Can ESP32-S3 use USB-to-Ethernet to provide wired network access?

The USB interface on ESP32-S3 operates in full-speed mode, with a maximum throughput of about 12 Mbps. It is therefore not suitable for directly attaching a USB-to-Ethernet chip to provide stable wired networking.

If Ethernet connectivity is required for ESP32-S3, an SPI-to-Ethernet solution is recommended instead.

When multiple devices use the ESP built-in USB-to-serial interface on the same PC, why do COM port numbers keep changing or increasing, and how can this be fixed?

This behavior is usually caused by Windows USB device enumeration. Windows identifies a USB device by combining its VID/PID descriptor and the physical port path, then records the assigned COM port number in the registry.

If multiple devices of the same model do not have unique USB serial numbers (iSerialNumber), Windows cannot distinguish them reliably. Each connection may be treated as a new device, so the COM port number keeps increasing.

The solution is to program a unique USB serial number for each device. Windows can then bind the COM port number to the serial number, making the port assignment stable even when the physical USB port changes.

Reference: How to keep a fixed COM port number for ESP USB devices