Q. Standards for scan codes ?
There are 3 standards for scan codes: Mode1 (83-key keyboard PC, PC-XT) and Mode2 (84-key AT keyboard) and Mode3 (101-key keyboard onwards). In Mode1 Make and Break codes are single bytes however different for same key. In Mode2 and Mode3 Make code is a single byte though Break code is two bytes (byte F0(Hex) + the make code).