Update README.md

README.md

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 # Exploded_Mini17
-STM32+CC1200 evaluation board
+This is an exploded version of the [Mini17](https://github.com/M17-Project/Mini17) UHF handheld tranceiver, a [TR-9](https://github.com/M17-Project/TR-9) successor. Its purpose is to allow for experimentation with the [CC1200](https://www.ti.com/product/CC1200) chip and its M17 use. In other words, it's an STM32+CC1200 evaluation board.
 
 <img src="https://github.com/M17-Project/Exploded_Mini17/blob/main/render.png?raw=true" width="500">
+
+## Flashing
+To enter the DFU mode, keep BTN2 pressed while powering the board up.
+
+## Hardware
+The Exploded Mini17 has all the peripherals a walkie-talkie development board should have:
+* GD32/STM32F405RGT6 micro with most of the unused pins available at the 2.54mm pin headers,
+* RF front end built around CC1200 chip,
+* 90° SMA connector,
+* set of 3 buttons,
+* microphone and a 1W speaker, along with amplifiers,
+* USB-C connector for programming and power supply.
+
+### Connector list
+
+| Designator   |  Function   | Remarks |
+|--------------|-------------|---------|
+|`CN1`|External power supply|6..15V|
+|`CN2`|External Button 1|Low-active|
+|`CN3`|External Button 2|Low-active|
+|`CN4`|External interrupt|Max. 3.3V|
+|`CN5`|External Button 3|Low-active|
+|`CN6`|External speaker output|≥8ohms, set `U6`/`U7` jumpers accordingly|
+|`CN7`|External microphone input|set `U10` jumper accordingly, bias provided by `U9`|
+|`H1`|GPIO port, 3 I/O lines|Max. 3.3V|
+|`H2`|SWD||
+|`H3`|GPIO port, 3 I/O lines|Max. 3.3V|
+|`H4`|GPIO port, 11 I/O lines|Max. 3.3V|
+|`H5/ANALOG`|Analog I/O port|Max. 3.3V|
+|`H6`|GPIO port, 6 I/O lines|Max. 3.3V|
+
+### Test point list
+| Designator   |  Function   | Remarks |
+|--------------|-------------|---------|
+|`TP1`|Speaker output signal, negative||
+|`TP2`|Speaker output signal, positive||
+|`TP3`|Audio DAC output signal||
+|`TP4`|Speaker amplifier input signal||
+|`TP5`|Microphone signal|DC-biased|
+|`TP6`|Amplified microphone signal|DC-biased|