diff --git a/const.h b/const.h
index 95d854d..51c8eb5 100644
--- a/const.h
+++ b/const.h
@@ -3,3 +3,6 @@
 #define VERTICAL_OFFSET 30
 #define HORIZONTAL_OFFSET 192
 #define LINE_BUFFER_SIZE 160
+
+#define BLACK 0x00
+#define WHITE 0xff
diff --git a/main.S b/main.S
index ff513ee..9e73528 100644
--- a/main.S
+++ b/main.S
@@ -2,14 +2,6 @@
 #include "macro.h"
 #include "const.h"
 
-.data
-
-frame:
-.word 0
-
-line:
-.word 0
-
 .text
 
 .global main
@@ -43,11 +35,12 @@ main:
     ldi r16, 1
     sts line, r16
 
-    call main_c
+    call setup_c
 
     sei                 ; global interrupt enable
 
 1:
+    call loop_c
     rjmp 1b
 
 .global int_horizontal_sync
diff --git a/main.c b/main.c
index 027d9fe..4590968 100644
--- a/main.c
+++ b/main.c
@@ -2,7 +2,9 @@
 #include <avr/interrupt.h>
 #include "const.h"
 
-char line_buffer[LINE_BUFFER_SIZE];
+volatile uint16_t frame;
+volatile uint16_t line;
+volatile char line_buffer[LINE_BUFFER_SIZE];
 
 ISR(INT0_vect, ISR_NAKED) {
     asm("jmp int_vertical_sync");
@@ -14,8 +16,23 @@ ISR(TIMER0_COMPA_vect, ISR_NAKED) {
     asm("jmp int_timer_0");
 }
 
-void main_c() {
+void setup_c() {
+    /*
     for (int i = 0; i < LINE_BUFFER_SIZE; ++i) {
         line_buffer[i] = (i % 2) ? 0x0 : 0xff;
     }
+    */
+}
+
+void loop_c() {
+    for (;;) {
+        const int current_line = line;
+        line_buffer[20] = (current_line > 50 && current_line < 100) ? WHITE : BLACK;
+        if (current_line % 8 == 0) {
+            const uint8_t current_number = frame >> 2;
+            for (uint8_t i = 0; i < 8; ++i) {
+                line_buffer[i] = ((current_number >> i) & 0x1) ? WHITE : BLACK;
+            }
+        }
+    }
 }