INT 2F - HEART.COM - INSTALLATION CHECK
        AX = D600h
Return: AX = 0303h (two hearts) if installed
            ES:DI -> buffer (see below)
Program: HEART.COM is a CPU lock-up/critical indicator utility by Mitch Davis.
Notes:  Once the host program has identified the address of the data area, it
          can change this to indicate safe/critical, alternate colours, etc.
        The entries for the color table are in char/attrib form.  Every two
          entries form a pair which is alternated between 68 times a minute.
          The first half of the table is for color videos, the second mono.
          Within each half, the first half is for the safe chars, and the
          second for the critical chars.

Format of buffer:
Offset  Size    Description
 00h  8 WORDs   table of colors/attributes (see notes above)
 10h    BYTE    flags
                bit 0: program is in critical section, so flash double
                        exclamation mark
                bit 1: program is in safe code, so flash the heart character
 11h    WORD    position of heartbeat on screen, normally 009Eh (last column
                of second line)

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