diff --git a/README.md b/README.md
index 070dbbf..d9860e3 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,6 @@
 # Seeed_Arduino_mbedtls  [![Build Status](https://travis-ci.com/Seeed-Studio/Seeed_Arduino_mbedtls.svg?branch=master)](https://travis-ci.com/Seeed-Studio/Seeed_Arduino_mbedtls)
+
+Please note that you need to use the following release versions for the respective firmware structures:
+
+- v2.0.1 - AT firmware structure
+- v3.0.1 and above - eRPC firmware structure