added cheatsheet "uart-connection.md"

cheatsheets/security/hardware/uart-connection.md

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+---
+title: UART Connection
+categories: [cheatsheets]
+tags: [security, hardware]
+---
+
+# UART Connection
+
+UART = Universal Asynchronous Receiver-Transmitter
+
+* Implements serial communication
+* Often a component of IC's
+* Uses 4 connections: GND | TX | RX | Vcc
+
+
+## Connecting to UART
+
+When connecting UART with e.g. an Computer, an additionall chip is needed to convert UART signals into a serial stream that can be read on a computer.
+A so called FNDI board is used for that task.
+
+### Connection
+
+* Vcc must not be connected
+
+```
+Chip <-> FTDI
+
+Tx  <-> Rx
+Rx  <-> Tx
+GND <-> GND
+```
+
+Input the FTDI board into the computer via USB.
+The USB-device should show up:
+
+```
+sh> lsusb
+[...]
+ Bus 002 Device 014: ID 0403:6001 Future Technology Devices International, Ltd FT232 Serial (UART) IC
+[...]
+```
+
+To communicate with that USB device, use `/dev/ttyUSB0`, or similar.
+Therefor `GNU/Screen` is used to interact with the device:
+
+```
+screen /dev/ttyUSB0 <baud-rate>
+```
+
+Common Baud rates are:
+
+* 9600
+* 19200
+* 28800
+* 57600
+* 115200
+
+
+## Identifying UART
+
+### With a multimeter
+
+* Meassure Voltage on the multimeter (`V - DC`)
+
+```
+Black: G,  Red: Vcc  -> ~3.3V or ~5V
+Black: G,  Red: Tx   -> ~3.3V +- 0.XV
+Black: G,  Red: Rx   -> 0V
+```
+
+## Identify BAUD rate
+
+### Guess
+
+* Just guess the most common baudrates by reconnecting with `screen`
+    * 9600
+    * 19200
+    * 28800
+    * 57600
+    * 115200
+
+### Logic Analyzer
+
+* TODO
+
+## How UART works?
+
+* Detailed Explanation: [Click here](https://www.allaboutcircuits.com/technical-articles/back-to-basics-the-universal-asynchronous-receiver-transmitter-uart/)