{----------------------------------------------------------------}
{                         ASYNC4U.PAS                            }
{                                                                }
{ This is a faithful translation of the famous ASYNC.INC by      }
{ Michael Quinlan into a Turbo 4.0 unit.  No extra frills,       }
{ no modification of types, nothing fancy.  But with this code   }
{ you should be able to delete your $I ASYNC.INC directive,      }
{ add a USES ASYNC4U statement, and recompile your existing      }
{ program.  If you want to add support for more ports, other     }
{ computers, or change to use the new data types, all good ideas,}
{ go right ahead. With this you don't have to.                   }
{                               Scott Gurvey, November 29 1987   }
{                                                                }
{ I have taken the liberty of modifying Scott's original         }
{ translation to make use of some of TURBO 4's nicer features.   }
{ To wit: The procedure that initializes this unit's variables   }
{ has been moved to the startup initialization section of the    }
{ unit, removing the need to call ASYNC_INIT.                    }
{ The unit now defines an ExitProc routine that will call        }
{ ASYNC_CLOSE whenever a termination occurs.  The procedure      }
{ ASYNC_CLOSE may still be explicitly called.  However, if an    }
{ abnormal termination should occur, the system won't be left    }
{ with interrupt handlers active.                                }
{                                Tom R. Donnelly, March 4, 1988  }
{----------------------------------------------------------------}
{                                                                }
{                         ASYNC.INC                              }
{                                                                }
{ Async Communication Routines                                   }
{ by Michael Quinlan                                             }
{ with a bug fixed by Scott Herr                                 }
{ made PCjr-compatible by W. M. Miller                           }
{ Highly dependant on the IBM PC and PC DOS 2.0                  }
{                                                                }
{ Moved Async_init into Unit Initialization Section              }
{ Setup ExitProc to call Async_close, to reset ports and         }
{ vectors                                                        }
{ based on the DUMBTERM program by CJ Dunford in the January     }
{ 1984 issue of PC Tech Journal.                                 }
{                                                                }
{ Entry points:                                                  }
{                                                                }
{   Async_Init                 (Moved to unit initialization)    }
{     Performs initialization.                                   }
{                                                                }
{   Async_Open(Port, Baud : Integer;                             }
{              Parity : Char;                                    }
{              WordSize, StpBits : Integer) : Boolean            }
{     Sets up interrupt vector, initialies the COM port for      }
{     processing, sets pointers to the buffer.                   }
{     Returns FALSE if COM port not installed.                   }
{                                                                }
{   Async_Buffer_Check(var C : Char) : Boolean                   }
{     If a character is available, returns TRUE and moves the    }
{       character from the buffer to the parameter               }
{     Otherwise, returns FALSE                                   }
{                                                                }
{   Async_Send(C : Char)                                         }
{     Transmits the character.                                   }
{                                                                }
{   Async_Send_String(S : LStr)                                  }
{     Calls Async_Send to send each character of S.              }
{                                                                }
{   Async_Close                                                  }
{     Turn off the COM port interrupts.                          }
{     **MUST** BE CALLED BEFORE EXITING YOUR PROGRAM; otherwise  }
{     you will see some really strange errors and have to re-boot}
{     (Note: The **MUST** restriction no longer applies.         }
{     This unit will hook itself into the ExitProc chain to      }
{     automatically close the com ports, if still open at)       }
{      termination.                                              }
{----------------------------------------------------------------}