diff --git a/ponydos.asm b/ponydos.asm
index bf81559..bf3c898 100644
--- a/ponydos.asm
+++ b/ponydos.asm
@@ -18,6 +18,12 @@ start:
 
 	sti
 
+	; Clear BSS
+	mov di, _bss_start
+	mov cx, _bss_end - _bss_start
+	xor al, al
+	rep stosb
+
 initialize_mouse:
 	; Initialize mouse
 	; https://www.ctyme.com/intr/rb-1601.htm
@@ -58,73 +64,92 @@ hang:
 	;int 0x10
 	jmp hang
 
+Y_OVERFLOW equ 0x80
+X_OVERFLOW equ 0x40
+Y_NEGATIVE equ 0x20
+X_NEGATIVE equ 0x10
+BUTTONS equ 0x03
+
+COLUMNS equ 80
+ROWS equ 25
+X_MAX_VALUE equ COLUMNS-1
+Y_MAX_VALUE equ ROWS-1
+
 mouse_handler:
 	push ax
 	push bx
 	push bp
+	push ds
+
+	mov ax, cs
+	mov ds, ax
 
 	mov bp, sp
 
-	; status
-	mov bx, [bp+16]
+	mov bx, [bp+18] ; status
 
-	; X negative
-	test bl, 0x10
-	jz .no_x_negative
-	mov ax, 0x0e00 + '-'
-	int 0x10
-	.no_x_negative:
+	test bl, X_OVERFLOW
+	jnz .x_end
+	.x:
+		mov ax, [bp+16] ; X
 
-	; X overflow
-	test bl, 0x40
-	jz .no_x_overflow
-	mov ax, 0x0e00 + 'o'
-	.no_x_overflow:
+		test bl, X_NEGATIVE
+		jnz .x_negative
+		.x_nonnegative:
+			add [mouse_x], ax
+			cmp word [mouse_x], X_MAX_VALUE
+			jb .x_end
+			mov word [mouse_x], X_MAX_VALUE
+			jmp .x_end
 
-	; X
-	mov ax, [bp+14]
-	call hexprint8
-	mov ax, 0x0e00 + ' '
-	int 0x10
+		.x_negative:
+			neg al
+			sub [mouse_x], ax
+			jnc .x_end
+			mov word [mouse_x], 0
+	.x_end:
+	mov ax, [mouse_x];debg
+	call hexprint16;debg
+	mov ax, 0x0e00 + ' ';debg
+	int 0x10;debg
 
-	; Y negative
-	test bl, 0x20
-	jz .no_y_negative
-	mov ax, 0x0e00 + '-'
-	int 0x10
-	.no_y_negative:
+	test bl, Y_OVERFLOW
+	jnz .y_end
+	.y:
+		mov ax, [bp+14] ; Y
 
-	; Y overflow
-	test bl, 0x80
-	jz .no_y_overflow
-	mov ax, 0x0e00 + 'o'
-	.no_y_overflow:
+		test bl, Y_NEGATIVE
+		jnz .y_negative
+		.y_nonnegative:
+			; Y-axis is inverted
+			sub [mouse_y], ax
+			jnc .y_end
+			mov word [mouse_y], 0
+			jmp .y_end
 
-	; Y
-	mov ax, [bp+12]
-	call hexprint8
-	mov ax, 0x0e00 + ' '
-	int 0x10
+		.y_negative:
+			neg al
+			add [mouse_y], ax
+			cmp word [mouse_y], Y_MAX_VALUE
+			jb .y_end
+			mov word [mouse_y], Y_MAX_VALUE
+	.y_end
+	mov ax, [mouse_y];debg
+	call hexprint16;debg
+	mov ax, 0x0e00 + ' ';debg
+	int 0x10;debg
 
-	; Left mouse
-	test bl, 0x01
-	jz .no_lmb
-	mov ax, 0x0e00 + 'L'
-	int 0x10
-	.no_lmb:
+	and bl, BUTTONS
+	mov [mouse_buttons], bl
 
-	; Right mouse
-	test bl, 0x02
-	jz .no_rmb
-	mov ax, 0x0e00 + 'R'
-	int 0x10
-	.no_rmb
-
-	mov ax, 0x0e00 + 13
-	int 0x10
-	mov ax, 0x0e00 + 10
-	int 0x10
+	mov al, [mouse_buttons];debg
+	call hexprint8;debg
+	mov ax, 0x0e00 + 13;debg
+	int 0x10;debg
+	mov ax, 0x0e00 + 10;debg
+	int 0x10;debg
 
+	pop ds
 	pop bp
 	pop bx
 	pop ax
@@ -162,3 +187,12 @@ hexprint4:
 times 510-($-$$) db 0
 db 0x55
 db 0xaa
+
+section .bss
+_bss_start:
+
+mouse_x resw 1
+mouse_y resw 1
+mouse_buttons resb 1
+
+_bss_end: