-extern void acm1602_locate_16x2(unsigned char addr, char x, char y);
-extern void acm1602_locate_8x2(unsigned char addr, char x, char y);
+extern void acm1602_locate_16x2(unsigned char addr, unsigned char x, unsigned char y);
+extern void acm1602_locate_8x2(unsigned char addr, unsigned char x, unsigned char y);