diff --git a/README.md b/README.md
index 47ad0bc..cd22ffe 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,9 @@ ESP-IDF V5.1 is required when using ESP32C6.
 
 # Hardware requirements
 - SN65HVD23x CAN-BUS Transceiver   
+SN65HVD23x series has 230/231/232.   
+They differ in standby/sleep mode functionality.   
+Other features are the same.   
 
 - Termination resistance   
 I used 150 ohms.