What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Opening a serial port can change the DTR and RTS control lines on your USB-to-UART bridge. On many ESP32 boards, those lines run through an auto-reset circuit to EN (also called CHIP_PU) and GPIO0, so a terminal that asserts them on connect can reset the chip. The fix depends on how your board is wired and which terminal and OS you use. This guide shows how to tell a port-open reset from a power or firmware fault, and what to change for each.
What is happening when the board resets
Espressif’s esptool documentation explains that DTR and RTS are used to reset an ESP32 into firmware download mode. The same page says: “Some OS and/or drivers may activate RTS and or DTR automatically when opening the serial port (true only for some serial terminal programs, not esptool), pulling them low together and holding the ESP in reset.” These signals are active low.
As an Amazon Associate I earn from qualifying purchases.
So a reset on port open is often expected hardware behavior, not a defect. It is not universal. Espressif ties it to some terminals and operating systems, and board circuits vary.
Recommended Free Tools
Three common wiring cases
| Board wiring | What it means for port-open resets |
|---|---|
| Two-transistor auto-reset circuit (DTR and RTS to GPIO0 and EN) | This is the arrangement in Espressif’s DevKitC schematic. Espressif says the circuit prevents a reset when both lines are asserted together. Other line combinations can still toggle EN, so the monitor’s DTR/RTS behavior matters. |
| RTS wired directly to EN | RTS/CTS hardware flow control can hold the board in reset. This is the case Espressif’s targeted advice covers. |
| No DTR/RTS connection, or different wiring | Auto-reset is unavailable. A reset on port open then points to something else, such as power or firmware. |
Typical USB-to-serial chips in this role include FTDI, CP210x and CH340x parts. Do not assume every product or revision routes the control lines identically. Find the schematic for your exact board and revision.
#1 Best Overall
- 2.4GHz Dual Mode WiFi + Bluetooth Development Board
- Support LWIP protocol, Freertos
- SupportThree Modes: AP, STA, and AP+STA
- Ultra-Low power consumption, Compatible with Arduino IDE
- ESP32 is a safe, reliable, and scalable to a variety of applications
Step 1: Confirm it is really a reset
Set the monitor to the baud rate your firmware uses. The ESP32 ROM boot log is at 115200 bps. Open the port and look for a fresh ROM message. Its second line includes a rst: reason and a boot: mode. A new ROM banner each time you connect means the chip restarted. If you see no banner, the board was probably already running and the monitor just started showing output.
Step 2: Identify your serial path and wiring
Work out whether your board has an onboard USB-to-UART bridge or whether you use a separate adapter. Then find the schematic or documentation. What you need to know is whether DTR and RTS reach EN and GPIO0 through the two-transistor circuit, whether RTS goes straight to EN, or whether neither is connected.
Step 3: Apply the fix that matches
RTS wired directly to EN
Disable RTS/CTS hardware flow control in your serial program. This is Espressif’s specific instruction for this wiring. It is not a universal setting for every ESP32.
Rank #2
- Dual-Core Performance Up to 240 MHz: Run sensor processing, wireless communication, automation logic and connected-device tasks on a 32-bit dual-core ESP32 platform designed for responsive embedded and IoT projects
- Built-in Wi-Fi and Bluetooth 4.2: Connect to 2.4 GHz Wi-Fi networks or use Bluetooth Classic and BLE for wireless sensors, smart devices, remote controls, home automation and other connected projects
- Flexible Power-Saving Modes: ESP32 power-management features support dynamic clock scaling and low-power operating modes, helping developers reduce energy use in compatible sensing, monitoring and connected-device applications, suitable for battery-powered Internet of Things (IoT) devices.
- USB-C Programming with CP2102: Connect through USB-C for power, sketch uploads and serial monitoring, while GPIO, UART, SPI and I2C interfaces support sensors, displays, motor drivers and other modules (USB-C cable not included)
- Over-the-Air Update Support: Configure OTA functionality through a compatible ESP-32 software framework to update deployed firmware over Wi-Fi without reconnecting the board by USB for every revision
Two-transistor auto-reset circuit
Don’t assume the direct-RTS explanation applies. Check how your monitor handles DTR and RTS on connect and compare that with the schematic. The reset may simply be the auto-reset circuit doing its job.
Linux
Espressif documents that Linux serial ports may assert RTS by default when nothing is attached. With the direct RTS-to-EN wiring above, that can hold an ESP32 in a reset loop. The documented remedy is to disable HUPCL. Treat this as a Linux-specific step tied to that wiring, not a general Windows or macOS fix.
Rank #3
- Powerful ESP-32 Board: Unlock the world of Internet of Things (IoT) and advanced electronics with the heart of this kit: the ESP-32 board. It features a powerful dual-core processor, integrated Wi-Fi and Bluetooth 4.2, making it perfect for building connected, smart devices that communicate with your phone or the cloud. It's fully compatible with the Arduino IDE for easy programming.
- Super Starter Kit: This kit contains over 35 different modules and electronic components, including sensors, displays, motors, and input devices. From LEDs and buttons to an OLED screen, servo motor, and keypad, you have everything needed to explore a vast range of projects in one box.
- Step by Step Online Tutorial: Jump right in with our detailed, beginner-friendly tutorial. Access 30+ projects with complete code, clear circuit diagrams, and step-by-step instructions. Learn the fundamentals of electronics, coding, and how to utilize the ESP-32's unique capabilities without any prior experience.
- Hands-on Learning for All Skill Levels: Perfect for students, makers, engineers, and hobbyists. Start with basic circuits and coding, then progress to intermediate and advanced IoT applications. Build practical projects like weather stations, smart home controllers, remote-controlled devices, and interactive gadgets. The skills you learn are the foundation for real-world innovation.
- Quality & Great Support: Elegoo is committed to quality. We provide a clear, detailed tutorial guide, refined code, and a well-organized component kit. All modules are carefully selected for reliability and ease of use. Our dedicated technical support team and active online community are ready to help you succeed in your learning journey.
EN capacitor
Espressif’s boot-mode documentation associates a 1–10 µF capacitor from EN to GND with reliable operation of the reset circuitry. Third-party boards differ, so don’t add one before checking the actual circuit. It is a board-specific repair, not a default purchase.
Step 4: If resets continue, rule out power and firmware
Not every reset is a serial-control issue. Espressif’s troubleshooting page recommends checking for stable 3.3 V power, pin voltages, devices attached to GPIO pins, and the early startup logs. It states that an ESP chip’s supply demand can reach up to 70 mA continuous and 200–300 mA at peak, possibly slightly higher. That is vendor guidance on the chip’s needs, not a measurement of your board.
Rank #4
- 2.4GHz Dual Mode WiFi + Bluetooth Development Board
- Support LWIP protocol, Freertos;ESP32 is a safe, reliable, and scalable to a variety of applications
- SupportThree Modes: AP, STA, and AP+STA
- Ultra-Low power consumption, Compatible with Arduino IDE
- 1PCS 30Pin ESP32 Development Board 2.4GHz WiFi Dual Cores Microcontroller Integrated with Antenna RF Low Noise Amplifiers Filters
The same page warns that some FTDI FT232R or Arduino 3.3 V outputs cannot supply enough current to power an ESP chip reliably. If you power the board from an adapter’s 3.3 V pin, check its current rating first. A multimeter is useful for checking EN and GPIO0 levels and watching the supply for dips.
If the rst: reason and the log show the chip restarting repeatedly regardless of how you connect, look at whether your firmware crashes right after boot.
Best Value
- 2.4GHz Dual Mode WiFi + Bluetooth Development Board
- Ultra-Low power consumption, works perfectly with the Arduino IDE
- Support LWIP protocol, Freertos
- SupportThree Modes: AP, STA, and AP+STA
- ESP32 is a safe, reliable, and scalable to a variety of applications
Flashing when auto-reset doesn’t work
This is separate from stopping monitor resets. On Espressif development boards, hold Boot (GPIO0) and press EN to enter firmware download mode. GPIO0 is sampled at reset to choose the boot mode. On other hardware, follow that board’s instructions. Espressif also describes pulling GPIO0 low.
An adapter that exposes both DTR and RTS is the easiest setup for automatic reset and flashing. Verify control-line support and power capability before relying on it.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
