INT 14H 03H: Query Serial Port Status

 Expects: AH    03H
          DX    COMM port number (0 to 3)
          ──────────────────────────────────────────────────────────────────
 Returns: AH    line status  ═╦══► see BIOS COM status codes
          AL    modem status ═╝
          ──────────────────────────────────────────────────────────────────
    Info: Obtains the current modem status and current line status for the
          specified COMM port.

See Also: INT 14H: Serial Port I/O
          Asynchronous Adapter Ports
          BIOS Data Area
          ROM-BIOS Functions
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