Update uart.md
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# UART
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## Table of contents
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### Summary
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* What is it ?
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* Identifying UART Ports
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* Connect to serial port
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* Detect baudrate
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* Interact with the /dev/ttyUSB0
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* UART over BLE
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* Examples
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* [UART](#uart)
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* [Table of contents](#table-of-contents)
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* [What is it ?](#what-is-it)
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* [Identifying UART ports](#identifying-uart-ports)
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* [Using a multimeter](#using-a-multimeter)
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* [Using a logic analyzer](#using-a-logic-analyzer)
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* [Connect to serial port](#connect-to-serial-port)
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* [WARNING](#warning)
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* [Examples](#examples)
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* [UART over BLE](#uart-over-ble)
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## What is it ?
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UART stands for Universal asynchronous receiver transmitter. Used for serial communications over a computer or peripheral device serial port.
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UART peripherals are commonly integrated in many embedded devices. UART communication makes use of baud rate to maintain synchronism between two devices. The baud rate is the rate at which information is transferred in a communication channel.
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@ -19,73 +22,111 @@ With access to the UART, a user can see bootloader and operating system logs.
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Generaly, the line is held high (at a logical 1 value) while UART is in idle state.
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We call the most common configuration 8N1 : eight data bits, no parity, and 1 stop bit.
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We call the most common configuration **8N1** : eight data bits, no parity, and 1 stop bit.
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## Identifying UART Ports
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## Identifying UART ports
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A UART pinout has four ports :
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- TX (Transmit)
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- Rx (Receive)
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- Vcc (Voltage)
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- GNR (Ground)
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A UART pinout has **four** ports :
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* **TX** (Transmit)
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* **RX** (Receive)
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* **Vcc** (Voltage)
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* **GNR** (Ground)
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To find UART multiple solution :
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- Search on Internet
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- Labeled on PCB
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- Find candidates
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- Use a multi-meter
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- Follow PCB traces (almost always impossible)
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* Search on Internet
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* Labeled on PCB
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* Find candidates
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* Using a multimeter
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* Using a logic analyzer
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* Follow PCB traces (almost always impossible)
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Keep in mind that some devices emulate UART ports by programming the Generla-Purpose Input/Output (GPIO) pins if there isn't enough space on the board for dedicated hardware UART pins.
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### Use a multimeter
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Keep in mind that some devices **emulate** UART ports by programming the General-Purpose Input/Output (GPIO) pins if there isn't enough space on the board for dedicated hardware UART pins.
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### Using a multimeter
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#### GNR pin
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First identify the GRN pin, by using the multimeter in continuity mode.
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Place the black probe on any grounded metallic surface, be it a part of the tested PCB or not. Then place the red probe on each of the ports. When you hear a beeping sound, you found a GND pin.
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#### VCC pin
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#### Vcc pin
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Turn the multimeter to the DC voltage mode in and set it up to 20V of voltage. Keep the black probe on a grounded surface. Place the red probe on a suspeted pin and turn on the device.
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If the multimeter measures a constant voltage of either 3.3V or 5V, you've found the VCC pin.
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If the multimeter measures a constant voltage of either 3.3V or 5V, you've found the Vcc pin.
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#### Tx pin
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Keep the multimeter mode at DC voltage of 20V or less, and leave the black probe in a grounded surface. Move the red probe to the suspected pin and power cycle the device. If the voltage fluctuates for a few seconds and then stabilizes at the Vcc value, you've most likely found the Tx pin.
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#### TX pin
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Keep the multimeter mode at DC voltage of 20V or less, and leave the black probe in a grounded surface. Move the red probe to the suspected pin and power cycle the device. If the voltage fluctuates for a few seconds and then stabilizes at the Vcc value, you've most likely found the TX pin.
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This behavior happens because, during bootup, the device sends serial data through that Tx pin for debugging purposes. Once it finishes booting, the UART line goes idle.
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This behavior happens because, during bootup, the device sends serial data through that TX pin for debugging purposes. Once it finishes booting, the UART line goes idle.
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#### Rx pin
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If you've already identified the rest of the UART pins, the nearby fourth pin is most likely the Rx pin.
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If you've already identified the rest of the UART pins, the nearby fourth pin is most likely the RX pin.
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Otherwise, you can identify it because it has the lowest voltage fluctuation and lowest overall value of all the UART pins.
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### Connect to serial port
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### Using a logic analyzer
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!!!!!!!!!!!!!!!DO THIS PART!!!!!!!!!!
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To find the UART pins we will connect the pins to a logic analyzer and look for data being transmitted. In the case of this device, bootloader and kernel logs are printed to this interface on startup, so we will expect to see data come across the transmit line of the UART device.2 This is what we will be looking for.
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https://medium.com/@shubhamgolam10/reverse-engineering-uart-to-gain-shell-de9019ae427a
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!!!!!!!!!!!!!!!DO THIS PART!!!!!!!!!!
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## Connect to serial port
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### WARNING
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It's not a big deal if you confuse the UART RX and TX ports with each other, because you can easily swap the wires connecting to them without any consequences. But confusing the Vcc with the GND and connecting wires to them incorrectly **might fry the circuit**.
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### Examples
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!!!!!!!!!!!!!!!REDO THIS PART!!!!!!!!!!
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Connect to UART using an USB to TTL, then find the `/dev/ttyUSB0` device in the `dmesg` command output. You need to create the `dialout` group for Debian or `uucp` for Manjaro :
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* `sudo usermod -a -G dialout username`
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* `sudo gpasswd -a username uucp`
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#### Detect baudrate
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!!!!!!!!!!!!!!!REDO THIS PART!!!!!!!!!!
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Standard baud rate are `110`, `300`, `600`, `1200`, `2400`, `4800`, `9600`, `14400`, `19200`, `38400`, `57600`, `115200`, `128000` and `256000`.\
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Auto-detect baud rate using the script : [devttys0/baudrate/baudrate.py](https://github.com/devttys0/baudrate/blob/master/baudrate.py)
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#### Detect baud rate
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##### Most common baud rate
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The most common baud rates for UART are `9600`, `19200`, `38400`, `57600` and `115200`.
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#### Interact with the /dev/ttyUSB0
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A table of other used but less common baud rates can be found here : [Here](https://lucidar.me/en/serialib/most-used-baud-rates-table/)
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```powershell
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cu -l /dev/ttyUSB0 -s 9600
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screen port_name 115200
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minicom -b 115200 -o -D Port_Name # to exit GNU screen, type Control-A k.
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microcom -d -s 9600 -p /dev/ttyUSB0
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microcom -d -s 19200 -p /dev/ttyUSB0
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##### Auto-detect the baud rate using a script
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Link : [baudrate.py](https://github.com/devttys0/baudrate/blob/master/baudrate.py)
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```bash
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# Download
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wget https://raw.githubusercontent.com/devttys0/baudrate/master/baudrate.py
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# Install serial
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pip2.7 install serial
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# Run the script on "/dev/ttyUSB0"
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python2.7 baudrate.py -p /dev/ttyUSB0
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```
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#### Interact with UART
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Different command line tools to interract with UART :
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```powershell
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cu -l /dev/ttyUSB0 -s 115200
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microcom -d -s 115200 -p /dev/ttyUSB0
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minicom -b 115200 -o -D /dev/ttyUSB0 # To exit GNU screen, type Control-A k
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screen /dev/ttyUSB0 115200
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```
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Script to brute force a password protected UART :
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```python
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import serial, time
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port = "/dev/ttyUSB0"
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baud = 9600
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baud = 115200
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s = serial.Serial(port)
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s.baudrate = baud
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@ -100,7 +141,7 @@ with open('/home/audit/Documents/IOT/passwords.lst', 'r') as f:
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time.sleep(10)
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```
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### UART over BLE
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## UART over BLE
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It’s an emulation of serial port over BLE. The UUID of the Nordic UART Service is `6E400001-B5A3-F393-E0A9-E50E24DCCA9E`. This service exposes two characteristics: one for transmitting and one for receiving.
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@ -114,8 +155,3 @@ Example with Micro::bit :
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* [https://makecode.microbit.org/v1/98535-28913-33692-07418](https://makecode.microbit.org/v1/98535-28913-33692-07418)
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* [Using the micro:bit Bluetooth Low Energy UART (serial over Bluetooth)](https://support.microbit.org/support/solutions/articles/19000062330-using-the-micro-bit-bluetooth-low-energy-uart-serial-over-bluetooth-)
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### Examples
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