DOS Fn 06H: Console I/O

                                                         Compatibility: 1.0+ 
 Expects: AH    06H
          DL    0 to 0feH   character to send to the Standard Output
                0ffH        request for input from the Standard Input
          ──────────────────────────────────────────────────────────────────
 Returns: ZF    clear (NZ) if character is ready ══╦═► on input requests
          AL    character read, if ZF is clear ════╝   (when DL=0ffH)
          ──────────────────────────────────────────────────────────────────
    Info: If DL is 0ffH, this performs a "no wait" console input, returning
          the Zero Flag (ZF) set (ZR) if there is no character ready.  If a
          character is ready, returns ZF cleared (NZ) with the character
          that was read in AL.

          If DL is anything but 0ffH, DL is sent to the Standard Output.

   Notes: ■ Does not check for Ctrl-Break.
          ■ Call twice for Extended ASCII.

See Also: Character I/O Functions
          DOS Functions
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