doc: update readme

README.md

@@ -8,6 +8,34 @@ Contains Internal Firmware programs of M5Stack Module PPS.
 
 **The last sector in STM32 stores calibration data. Modifying the content of this sector will make the module unable to function normally.**
 
+## How to backup calibration data
+
+1. Open STM32CubeProgrammer and use STLink to connect to Module PPS
+
+2. Connect to Module PPS
+
+3. Set the address to 0x08007800 and the size to 0x800
+
+4. Save as hex file
+   
+   ![](./imgs/step1.png)
+   
+   ![](./imgs/step2.png)
+
+## How to restore calibration data
+
+1. Open STM32CubeProgrammer and use STLink to connect to Module PPS.
+
+2. Connect to Module PPS
+
+3. Chose hex file (Note that the address is 0x8007800 and the size is 2048 Bytes)
+
+4. Cancel "Full chip erase"
+
+5. Start Programming
+   
+   ![](./imgs/step3.png)
+
 ## License
 
 [M5Module-PPS-Internal-FW - MIT](LICENSE)