diff --git a/main.c b/main.c
index b4a61f7..95d20fd 100644
--- a/main.c
+++ b/main.c
@@ -9,6 +9,17 @@
 #include "lib/7segment.h"
 #include "lib/7segment_4digits.h"
 
+/**
+ *       O O O O O O O O
+ * DDRF  x x x x x x x x
+ *       \-\-\-\-\-\-\-\--- 7 segment output
+ * 
+ *      I I O O O O O O
+ * DDRK x x x x x x x x
+ *      | |     \-\-\-\--- digit selection output
+ *      \-\--------------- Button input
+*/
+
 void main() {
     DDRF  = 0b11111111;
     DDRK  = 0b00001111;