diff --git a/C64_4joy_adapter/README.md b/C64_4joy_adapter/README.md
index 9ebb49d..c73bf55 100644
--- a/C64_4joy_adapter/README.md
+++ b/C64_4joy_adapter/README.md
@@ -36,6 +36,7 @@ sei
 ## avr asm
 - http://www.nongnu.org/avr-libc/user-manual/inline_asm.html
 - https://ucexperiment.wordpress.com/2016/03/04/arduino-inline-assembly-tutorial-1/
+- https://ucexperiment.wordpress.com/2016/03/11/arduino-inline-assembly-tutorial-5-2/
 
 ## register as variable
 - https://forum.arduino.cc/index.php?topic=43760.5