Seeed Arduino Serial

Serial communications provide an easy and flexible way for your Arduino board to interact with your computer and other devices. Implementing serial communications involves hardware and software. The hardware provides the electrical signaling between Arduino and the device it is talking to. The software uses the hardware to send bytes or bits that the connected hardware understands.

Most of arduino boards have at least one Serial, some have multiple serials(Arduino Mega has 4 Serials).

It communicates on digital pins 0 (RX) and 1 (TX) as well as with the computer via USB. So if you connect UART device on pin 0 and pin D1, you have to remove them before downloading program through USB. Or else it will cause upload fails.

Sometimes you need more serial ports than the number of hardware serial ports available. If this is the case, you can use an Software Serial that uses software to emulate serial hardware. Software serial requires a lot of help from the Arduino controller to send and receive data, so it’s not as fast or efficient as hardware serial.

Some boards, such as the Seeeduino Stalker V3.1 and Seeeduino Ethernet, do not have USB support and require an adapter for connecting to your computer that converts TTL to USB.


The TX/RX uses TTL logic levels(5v/3.3v). You can not connect it directly to RS232 serial port, which operates at ±12v. You need the TTL to RS232 converter to change the voltage levels.

BOARDs Micro Controller USB Serial Hardware Serial
Seeeduino V4.2, Seeeduino Lotus Atmega328 Serial Serial: 0(RX), 1(TX)
Seeeduino Mega Atmega2560 Serial Serial: 0(RX), 1(TX) Serial1: 19(RX), 18(TX) Serial2: 17(RX), 16(TX) Serial3: 15(RX), 14(TX)
Seeeduino Ethernet, Seeeduino GPRS Atmega328P Need USB to TTL adapter Serial: 0(RX), 1(TX)
Seeeduino GPRS Atmega32U4 Serial Serial: 0(RX), 1(TX)
Seeeduino Cloud Atmega32U4 Serial Serial: 0(RX), 1(TX), Grove UART port and Dragino module HE
Seeeduino Lite Atmega32U4 Serial Serial1: 0(RX), 1(TX)
Seeeduino LoraWAN ATSAMD21G18 SerialUSB Serial: Connect to GPS module Serial1: Connect to RHF76-052AM for AT commands and 0(RX), 1(TX) SerialDebug: Connect to RHF76-052AM for firmware update
Seeeduino Lotus Cortex-M0+ ATSAMD21 SerialUSB Serial: Connect to J2 UART Grove Port Serial1: Connect to 0(RX), 1(TX)
Wio Link ESP8266 Serial Serial:Connect to UART Grove Port
Wio Tracker - GPS, BT3.0, GSM, Arduino Compatible ATSAMD21G18A SerialUSB SerialDBG: Connect to Grove UART Port serialMC20: Connect to MC20
Wio LTE Cat.1 STM32F405RG SerialUSB serialDebug: Connect to EC21 Serial: Connect to Grove UART Port
Wio LTE Cat M1/NB-IoT Tracker STM32F405RG SerialDebug SerialGrove: Connect to Grove UART Port SerialGSM: Connect to LTE M1/NB-IOT module SerialGNSS: Connect to GPS module

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