when the buffer is more than three-quarters full.
                            If handshaking is enabled, it is an error for the
                            application to adjust the line by using the
                            Win32 EscapeCommFunction function.

                      input buffer | less than 1/2 full | more than 3/4 full
                     --------------+--------------------+--------------------
                        RTS        | output set         | output clear   

      TransmissionAvailable
                            Specifies that the RTS line will be enabled
                            if bytes are available for transmission. After
                            all buffered bytes have been sent, the RTS line
                            will be disable.

                      output buffer | have available byte | no any data
                     ---------------+---------------------+----------------- 
                        RTS         | output set          | output clear

      RTS is a output pin. You can set its state in MCR register.
      It usually connect to CTS pin in the other end.
      You can change this value when the comm is open.

  XonLimit : WORD

      Specifies the minimum number of bytes allowed in the input buffer
      before the XON character is sent.
      You can change this value when the comm is open.

      Example:
          The size of input buffer is 1000 bytes and XonLimit is 100.
          And XOff character have sent before.
          When bytes in input buffer from 101 to 100, the Xon character is
          sent.

  XoffLimit : WORD

      Specifies the maximum number of bytes allowed in the input buffer
      before the XOFF character is sent. The maximum number of bytes
      allowed is calculated by subtracting this value from the size,
      in bytes, of the input buffer.
      You can change this value when the comm is open.

      Example:
          The size of input buffer is 1000 bytes and XonLimit is 100.
          When bytes in input buffer from 899 to 900, the Xoff character is
          sent.

  ByteSize : ( _5, _6, _7, _8 )

      Specifies the number of bits in the bytes transmitted and received. 
      You can change this value when the comm is open.

  Parity : ( None, Odd, Even, Mark, Space )

      Specifies the parity scheme to be used. This member can be one of the
      following values:

      Value   Meaning
      ------- ---------------------
      None    No parity
      Odd     Sum of logic '1' bits (data bits and parity bit) is odd
      Even    Sum of logic '1' bits (data bits and parity bit) is even
      Mask    Parity bit is always in logic '1'
      Space   Parity bit is always in logic '0'

      You can change this value when the comm is open.


  StopBits : ( _1, _1_5, _2 )

      Specifies the number of stop bits to be used.
      You can change this value when the comm is open.

  XonChar : AnsiChar

      Specifies the value of the XON character for both transmission and
      reception.
      You can change this value when the comm is open.

  XoffChar : AnsiChar

      Specifies the value of the XOFF character for both transmission and
      reception.
      You can change this value when the comm is open.

  ReplacedChar : AnsiChar

      Specifies the value of the character used to replace bytes received
      with a parity error when ReplaceWhenParityError member is TRUE and
      ParityCheck member is TRUE.
      You can change this value when the comm is open.

  Handle : THandle   <read-only>

      The comm file handle. Get from 'CreateFile' function in 'StartComm'.
      You can use it for another Win32 COMM API operation

  SendDataEmpty : Boolean   <run-time & read-only>

      True when send-buffer is empty and no any pending send require in message
      queue. False if send-buffer is not empty or have send require in message
      queue.

METHOD
======

  procedure StartComm

      Start a communication for this comm port.
      If failure, raise ECommsError exception and ECommsError.Message contain
      following string:
          'This serial port already opened'
          'Error opening serial port'
          'File handle is not a comm handle'
          'Cannot setup comm buffer'
          'Unable to create event'
          'Unable to create read thread'
          'Unable to create write thread'

  procedure StopComm

      Stop and end all communication threads for this comm port.
      No any return.

  function WriteCommData( pDataToWrite: PChar;
                          dwSizeofDataToWrite: Word ): Boolean

      Send a String to the Write Thread to be written to the Comm.
      This subroutine will return immediately. The send operation will
      do in background.
      Parameters:
          pszStringToWrite     - string to Write to Comm port.
          nSizeofStringToWrite - length of pszStringToWrite.
      Return:
          TRUE : if the PostMessage to write thread is successful.
          FALSE: if PostMessage fails or Write thread doesn't exist.

  function GetModemState : DWORD;

     Get and return the modem state right now. They are the state of modem
     input pin from MSR.
     The return value can be one or more of the following codes:

      Value       Meaning
      ----------  -----------------------------------------------------------
      MS_CTS_ON   The CTS (clear-to-send) signal is on.
      MS_DSR_ON   The DSR (data-set-ready) signal is on.
      MS_RING_ON  The ring indicator signal is on.
      MS_RLSD_ON  The RLSD (receive-line-signal-detect) signal is on.

      The function fails if the hardware does not support the
      control-register values.

EVENT HANDLER
=============

  OnReceiveData : procedure (Sender: TObject;
                             Buffer: Pointer;
                             BufferLength: Word) of object

      When
        1. The input buffer contains received data and
        2. more than a limit size or
        3. read time-out
      the event handler is called
      Sender : point to TComm object which raise this call
      Buffer : the buffer which contains received data
      BufferLength : the size of received data in Buffer

  OnReceiveError : procedure(Sender: TObject; EventMask : DWORD) of object

      When error happend during receiving, the event handler is called.
      Sender : point to TComm object which raise this call
      EventMask : the value get from ClearCommError in 'HandleCommEvent'
                  A 32-bit variable to be filled with a mask indicating the
                  type of error. This parameter can be one or more of the
                  following error codes:

      Value       Meaning
      ----------  -----------------------------------------------------------
      CE_BREAK    The hardware detected a break condition. (no support now)
      CE_DNS      Windows 95 only: A parallel device is not selected.
      CE_FRAME    The hardware detected a framing error.
      CE_IOE      An I/O error occurred during communications with the device.
      CE_MODE     The requested mode is not supported, or the hFile parameter
                  is invalid. If this value is specified, it is the only
                  valid error.
      CE_OOP      Windows 95 only: A parallel device signaled that it is out
                  of paper.
      CE_OVERRUN  A character-buffer overrun has occurred. The next character
                  is lost.
      CE_PTO      Windows 95 only: A time-out occurred on a parallel device.
      CE_RXOVER   An input buffer overflow has occurred. There is either no
                  room in the input buffer, or a character was received after
                  the end-of-file (EOF) character.
                  (second condition is impossible happened under Win32)
      CE_RXPARITY The hardware detected a parity error. (no support)
      CE_TXFULL   The application tried to transmit a character, but the
                  output buffer was full. (no support)


  OnRequestHangup: procedure(Sender: TObject) of object;

      When the program is terminated abnormally, the event handler is
      called.

  OnModemStateChange : procedure(Sender: TObject; ModemEvent : DWORD) of object

      When Modem's RLSD(CD) change state (HIGH<->LOW) or the ring indicator
      signal is detected, this event handler is
      called.
      Sender : point to TComm object which raise this call
      ModemEvent : A 32-bit variable to be filled with a mask indicating
                   what made this call. This parameter can be one or more
                   of the following codes:

      Value       Meaning
      ----------  -----------------------------------------------------------
      ME_CTS      The CTS (clear-to-send) signal has changed state.
                  (support in future, not support now)
      ME_DSR      The DSR (data-set-ready) signal has changed state.
                  (support in future, not support now)
      ME_RING     The ring indicator signal was detected.
      ME_RLSD     The RLSD (receive-line-signal-detect) signal has changed
                  state.

      Call GetModemState method to get the real state of modem state.

LEGALITIES
==========

This component is totally free (along with source code).

Small-Pig Team
29/4/97
E-mail:  spigteam@vlsi.ice.cycu.edu.tw