INT 15 - CASSETTE - READ DATA (PC and PCjr only)
        AH = 02h
        CX = number of bytes to read
        ES:BX -> buffer
Return: CF clear if successful
            DX = number of bytes read
            ES:BX -> byte following last byte read
        CF set on error
        AH = status (see below)
SeeAlso: AH=00h"CASSETTE",AH=03h"CASSETTE"

Values for status:
 00h    successful
 01h    CRC error
 02h    bad tape signals
 04h    no data
 80h    invalid command
 86h    no cassette present

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