Questions tagged [uart]

a Universal Asynchronous Receiver/Transmitter, better known as serial port

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39 votes
11 answers
65k views

How to get more than one uart interface

Ok, I have one uart interface (TXD GPIO 14, RXD GPIO 15). I want at least one more uart interface. Possible solutions: Bit banging: Use two unrelated spare GPIOs. I understand that timing is a ...
  • 625
16 votes
3 answers
2k views

How do I connect my printer to the serial GPIO pins?

I've purchased a Mini Thermal Printer from Adafruit. The documentation states: This printer is ideal for interfacing with a microcontroller, you simply need a 3.3V to 5V TTL serial output from ...
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14 votes
5 answers
15k views

Disable DTR on ttyUSB0

I'm connecting from Pi to Arduino-clone board. The problem is, that I need to disable DTR line, in order to prevent Arduino from resetting on connect. I have read that on RPi is not possible to ...
  • 324
14 votes
2 answers
56k views

How can I set the UART speed?

How should you set the baud rate of the UART Bonus question: What baud rates are available on the RPi? Edit: Since reading up from Steve's answer, I have found that there are two UARTs available. ...
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11 votes
2 answers
18k views

PiGPIO Library Example for Bit-Banging a UART

The PiGPIO library http://abyz.me.uk/rpi/pigpio/index.html mentions that one of it's features is "software serial links using any user gpio". I take this to mean that you can use it to generate a ...
  • 361
10 votes
7 answers
11k views

True 9-bit serial port data?

I have an existing, half complete, vending machine project running on an Atmel UTC, which I want to port to the Pi. In order to talk to peripherals, such as coin acceptor, it has to support Multi-...
10 votes
1 answer
4k views

Pi 4 I/O interface options... and where to find them

The BCM2711's hardware documentation lists multiple I/O interface options. Among others these are: up to 6 × I2C, up to 6 × UART (muxed with I2C), up to 6 × SPI (only five exposed on Raspberry Pi ...
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8 votes
2 answers
35k views

Where are the uarts on the raspberry pi 4?

The raspberry pi 4 has at least two uarts (as shown here), I know where I can connect to one of them. Pins 8, 10 and 12 have a uart as an option. Source: This site describes accessing uart1, where ...
8 votes
3 answers
29k views

How to connect SIM800 GSM ADD-ON to RaspberryPi 3

I am confused about how to connect SIM800 GSM module to RaspBerry PI 3. I connect the module to RaspBerry PI using the GPIO pins. What happends now? Are those GPIO pins automatically connected to ...
7 votes
1 answer
480 views

Bit waveform clarification

I have been trying to learn more about bit transmission through the uart, and I have the following code in python to transmit information: import serial ser = serial.Serial( port='/dev/ttyAMA0',...
7 votes
2 answers
6k views

Is there a way to make a regular GPIO pin into a Tx UART pin?

I'm working on a project that is going to need two different UART interfaces. Is there a way to make a regular GPIO pin into a Tx UART pin, I don't need an Rx pin too. Is there a software solution ...
6 votes
2 answers
5k views

Virtual UART ports

I want to use a Rpi to interface with 3 atmega ics in an embedded system but the pi seems to only have one uart port. I know arduino can emulate a serial connection over two io pins, will this be ...
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6 votes
2 answers
3k views

UART Output working on 57600 Baud but with 115200 only gibberish

I've got a strange problem with serial output. Using Wheezy and 8 Databits, 1 Stopbit, NoFlowcontroll, NoParity (config as stated in eLinux Wiki). With 57600 Baud everything works fine but with 115200 ...
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6 votes
1 answer
5k views

UART RX stops reading data after working correctly

I'm trying to read an continuous stream of data from my device (laser altimeter). The device is connected to the UART Rx pin of raspberry Pi 3B+. Everything works fine with this python code: import ...
6 votes
1 answer
15k views

How to communicate between Pi 3 and an Arduino using UART from GPIO?

I need to transfer data between Arduino and Pi. I have an Pi 3, and I used a simple circuit with a voltage divider to deal with 3.3v vs 5v logic levels. But I got nothing. Then, I used only Pi3 with ...
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5 votes
4 answers
12k views

Connect sim800 to Raspberry PI (RX, TX)

I've been trying to connect my sim800L to my Raspberry pi 3 model B (rasbian) but without success... I'm at the very first step, and since I'm new to Raspberry pi, I don't understand very well how it ...
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4 votes
2 answers
2k views

Binary garbage on the UART when powering the RPi

I have a strange issue I cannot figure out. I have a thermal printer (https://www.adafruit.com/products/597) plugged to the UART (/dev/ttyAMAO). I configured the RPi to remove the console on /dev/...
4 votes
2 answers
2k views

Impact of using UART

I'm trying to understand the impact of using UART communication of the Raspberry's GPIO pins. So I'm reading the Raspberry UART documentation, but I'm not sure if I get everything right. It says: ...
4 votes
1 answer
1k views

How do I use a Raspberry Pi to install OpenWrt firmware on a BT HomeHub 5a or PlusNet Hub One router

I have a spare BT HomeHub 5a clone (actually a PlusNet Hub One router). I would like to install the OpenWRT firmware on it, in order to reliably use it as a wired wifi range extender without a DHCP ...
4 votes
2 answers
5k views

How should I properly communicate 2 Raspberry Pi via UART?

I'm testing serial communication with Python pyserial module. I try to communicate some strings between two Raspberry Pi's ... I tested transmitter and receiver code at same device connecting it's ...
4 votes
2 answers
65k views

How can I test if the serial / UART is good on a Raspberry Pi?

I've purchased a used Raspberry Pi and have followed the instructions from Wolf Paulus's Journal to connect to the Raspberry Pi from my computer using a PL2303 USB adapter. The specifications on the ...
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4 votes
3 answers
2k views

ttyAMA0 disabled but still shows one boot message

I'm trying to use the UART for my own purposes. I'm using Raspbian I've edited cmdline.txt and inittab but I still get the one line message Uncompressing Linux... done, booting the kernel. How do ...
  • 143
4 votes
3 answers
14k views

UART serial interrupt routine

Is there a simple way to use the registers as an interrupt trigger? I can make the application run in a new pid and poll for serial input using fork() I just need to read data, no write needed This ...
4 votes
1 answer
28k views

Identifying USB devices [closed]

I have several RS232 to TTL UART converters plugged into my Pi. The problem is that their device assignments change sporadically. Sometimes the first device gets /dev/ttyUSB0, and another time /dev/...
4 votes
1 answer
3k views

Bluetooth UART on the Compute Module

We're trying (unsuccessfully) to attach a UART bluetooth SoC to the Raspberry Pi 3 Compute Module. The bluetooth SoC is a based off a Nordic nRF51. It's running project Zephyr RTOS hci_uart sample. ...
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3 votes
4 answers
78 views

raspberry pi voltage rs-232 (uart)

I am trying to configure a sensor with serial communication (raspberry-sensor). But i have connected my sensor to a oscilloscope see photo. I don't know if i can connect it directly to my rspberry pin ...
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3 votes
2 answers
825 views

Does a UART connection require shared ground?

I'm a novice with electronics but not Linux. This situation has had me scratching my head for two nights. I connected a Pi Pico to a Raspberry Pi 4 via UART, and managed to receive messages sent from ...
3 votes
3 answers
2k views

RPi 4 -- Garbage on serial console (UART) using upstream kernel

I'm experimenting with upstream kernel and now I try to get serial console working. I'm getting only garbage symbols when I try to communicate: I think it is important to notice that I only get ...
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3 votes
1 answer
157 views

Is Fingerprint Scanner TTL (GT-511C3) compatible with Raspberry Pi Zero?

I have a question regarding Fingerprint Scanner - TTL (GT-511C3). Here is a link. Is this fingerprint scanner compatible with Raspberry Pi Zero?
3 votes
2 answers
3k views

9 Data Bits on UART pins?

I am wondering if it is possible to send 9 data bits framed with a start/stop bit at 1.25MBaud. I am currently using PySerial to configure the UART pins on the pi. I've stumbled across a few ...
3 votes
1 answer
5k views

Why am I seeing some garbage bytes at the serial console login?

When I log into my serial console using screen /dev/ttyUSB0 115200, I see some garbage in the output: �� Arch Linux 3.6.11-10-ARCH+ (ttyAMA0) raspberry login: root �Password: Login incorrect ...
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3 votes
1 answer
2k views

How can I disable the serial console on distributions that use U-Boot?

I'm trying to use a Raspberry Pi with a UART peripheral and a non-Raspbian Linux distribution. It seems like most of these distributions use U-Boot. I'm running into two problems: U-Boot outputs on ...
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3 votes
2 answers
160 views

Why is UART-USB link inserting many unexpected bytes when using /dev/serial0 with dev/ttyUSB0?

My first post and my first Pi project. I'm experimenting with data transfer between Pi and external UART-enabled devices. As part of this, I want to prototype simple bi-directional data transfer ...
  • 61
3 votes
1 answer
2k views

Can I use the TX/RX pins and the USB ports for multiple serial devices?

I have two devices I want to use (GPS module and a PM2.5 sensor) that both use serial communication. I know you can't throw two devices on the same serial line. However, I've seen some badly explained ...
3 votes
1 answer
658 views

Adafruit Ultimate GPS HAT Connections

I have been messing around with this GPS HAT for a few days now. I do have it working, although I have multiple modules running at once on stacked breadboards. My main question is on AdaFruit's ...
3 votes
2 answers
5k views

Rpi to Arduino Serial UART Communication Tutorial

I'm trying to connect my Arduino to my Raspberry Pi using the GPIO pins. I understand that the Pi uses a 3.3V signal while the Arduino uses a 5V signal so I bought a bi-directional logic level ...
  • 141
3 votes
3 answers
10k views

How to set non standard serial port speed

I need to set the serial port /dev/ttyS0 to 250k bit/sec in order to send commands to another device expecting 250k. I am using Python and trying to set the speed with the command ser=serial.Serial( ...
  • 131
3 votes
5 answers
20k views

UART problems on my Pi3

I am trying to send and receive radio signals using my Raspberry, but I am already stuck at the first step :) My Radio module uses UART for communication but I have failed to set up my serial ...
  • 193
3 votes
1 answer
6k views

Pi 3 Boot with UART console

I use Raspberry Pi 3 with image "RASPBIAN JESSIE" which is 2016-02-26 build. I plug in micro-usb to power on. Then I use USB to TTL adapter to try to login. I've set baud rate 115200, and connect GND, ...
3 votes
1 answer
659 views

Strange issue on UART (via FTDI USB <--> RS-232 adapter)

I'm trying to establish a high speed UART communication. Since ttyAMA0 is not quite good at 1+ Mbaud, decided to use FTDI adapter (based on FT232RL chip) instead. I've tested an adapter on my laptop ...
3 votes
1 answer
2k views

Redirecting stdout and stderr to UART

I am building my own cross-linux-from-scratch (CLFS) system for Raspberry Pi. I already build whole system, I prepared SD card and now I try to boot. I am redirecting all kernel output to serial ...
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3 votes
1 answer
450 views

Strange behavior when using UART0

I need to use all five of the PL011 UARTs on a Raspberry Pi 4. I am having no problems with UART2 - UART5. It is only UART0 that is giving me problems. I connect a serial cable from a laptop to the ...
  • 143
3 votes
1 answer
3k views

Sim800 not responding to AT commands

I have a Sim800 GSM module hooked up to pins 8 and 10 of the a PI B+ running the latest version of Jessie. I have configured Jessie so that nothing else is using the TXD0 and RXD0 pins. If I connect a ...
3 votes
1 answer
955 views

UART cannot send

UART on my pi cannot send data, I can receive data from another machine, but I cannot send any data using the 'tx' pin of UART. I also try to connect 'tx' and 'rx' on my pi, but still no data is sent ...
3 votes
1 answer
1k views

Serial USB-RS485 failing to read on Pi but not on Ubuntu laptop?

I am reading values from a Battery Management System using two, serial USB-RS485 adaptors (ftdi). I am doing this over MODBUS using the minimal modbus library and python: # Bank A # port name, slave ...
3 votes
1 answer
373 views

uart issue in pi-3

I have a problem regarding the uart not working at all, following are the steps as done from my side. updated and upgraded the raspberry pi,initially i installed raspbian wheezy to sd card and i am ...
3 votes
2 answers
2k views

Serial Communication between Raspi and Arduino Mega

I apologize for the double post, but I asked this question earlier and somehow it does not appear under my user and I can't make any edit or comments to it: Trouble with UART Serial Communication with ...
3 votes
1 answer
4k views

Raspberry pi, how to debug rx, tx pin

I have made a program which give instruction to a motor module. I have successfully send instruction to him, asking it to make a rotation back and forth, but I can't get back the feedback result. I ...
3 votes
0 answers
635 views

Bare Metal RPI 3B UART not working

I have referred many tutorials to get UART working in bare metal environment on RPI 3. https://github.com/dwelch67/raspberrypi/tree/master/uart05 https://github.com/mrvn/RaspberryPi-baremetal/tree/...
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3 votes
0 answers
5k views

Raspberry Pi and LIN Bus

I want to implement a LIN Bus using a Raspberry Pi 3. The RPi will be the master controlling slaves on the LIN Bus. My idea is to use the Raspberry Pi UART, but I am not sure to what extent this ...

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