diff --git a/avr-gcc-toolchain.cmake b/avr-gcc-toolchain.cmake
index 186e108..923157d 100644
--- a/avr-gcc-toolchain.cmake
+++ b/avr-gcc-toolchain.cmake
@@ -16,9 +16,10 @@ set(AVR_MCU attiny13a)
 
 #set(F_CPU 16000000UL)
 #set(F_CPU 8000000UL)
-#set(F_CPU 9600000UL)
-set(F_CPU 1200000UL)
-#set(F_CPU 4800000UL)
+#set(F_CPU 9600000UL)#AVR without prescaler
+set(F_CPU 1200000UL) #AVR (9.6MHz) with prescaler 8DIV
+#set(F_CPU 4800000UL) #AVR without prescaler
+#set(F_CPU 600000UL) #AVR (4.8MHz) with prescaler 8DIV
 
 add_compile_definitions(F_CPU=${F_CPU})
 # add_compile_definitions(MCU=atmega328p)