diff --git a/README.md b/README.md
index 117446d..9740b78 100644
--- a/README.md
+++ b/README.md
@@ -39,3 +39,8 @@
  - A bat file that modifies the Index HMD firmware and creates Watchman Dongle firmware for nrf52840.
  - Generate uf2 and bin files.
  - Index HMD's four boot modes can be changed without hardware modification.
+
+# About SD_gen.bat
+Firmware generated by FW_gen.bat only works with softdevice s140 v6.1.1.   
+Some nRF52840 boards (e.g. seeed xiao nRF52840) use newer versions such as v7.3.0.   
+In those cases, please use SW_gen.bat to create and write a uf2 file for v6.1.1 softdevice.