Worker thread pausing

//I am using Visual C++ 6 (working on upgrading soon)

//At the top I have:
UINT SerialThread( LPVOID Param );

//In the BEGIN_MESSAGE_MAP(...) I added:
  ON_MESSAGE(MY_SERIAL, DataPresent)
  ON_MESSAGE(MY_UNIT, DataUnit)

//In OnInitDialog() I have added:
  AfxBeginThread(SerialThread,(LPVOID)m_hWnd);

//Actual thread to monitor serial activity:
UINT SerialThread( LPVOID Param ) //Thread to monitor serial activity
{
  HWND hDlg = (HWND)Param;
  int DataByte=0x00;
  int i;

  ercount=0;
  while(TRUE){
    ercount=0;
    while(ercount == 0){
      ercount = BytesInReceiveBuffer(m_Port);
      Sleep(50);
    }
    DataByte=GetByte(m_Port);
    if (DataByte == 0x10){ // if 1st byte was 10h ignore next
33 bytes
      for (i=0; i<33; i++){
        DataByte=GetByte(m_Port);
      }
    }
    if (DataByte == 0x11){ // if 1st byte was 11h read and save
next 33 bytes
      for (i=0; i<33; i++){
        DataByte=GetByte(m_Port);
        Bar[i]=(DataByte & 0xff); // Bar[] is a global unsigned char
string of 33 bytes
      }
      RunRead=1; // global variable I look for in
some loops to wait for data
      ::PostMessage(hDlg, MY_SERIAL, (WPARAM)0, (LPARAM)0);
    }
    if (DataByte == 0x20){ // if 1st byte was 20h read and save
next 1 byte
      DataByte=GetByte(m_Port);
      UnitSel=DataByte;
      ::PostMessage(hDlg, MY_UNIT, (WPARAM)0, (LPARAM)0);
    }
  }
  return TRUE;
}

//RunRead is what I tried to us to let another routing know when data was
received.

//MY_SERIAL - updates a bargraph with the 33 bytes received

//MY_UNIT - updates a unit number

//How do I temporarily stop this thread so another area of the dialog can
control the serial port ??
//Example: I have a routing that sends a byte out the serial port to an
external microcontroller
// and I want to wait for the response within this routine...