INT 15 - CASSETTE - WRITE DATA (PC and PCjr only)
        AH = 03h
        CX = number of bytes to write
        ES:BX -> data buffer
Return: CF clear if successful
            ES:BX -> byte following last byte written
        CF set on error
        AH = status (see AH=02h"CASSETTE")
        CX = 0000h
SeeAlso: AH=02h"CASSETTE"