If a general failure error is not returned, the physical device driver returns valid information in the Data Packet. The general Device Control Block (DCB) parameter access Functions 53h and 73h are used for:

• Automatic Transmit Flow Control (start/stop transmit when XON/XOFF character received)
  
• Automatic Receive Flow Control (transmit XON/XOFF when receive buffer fills or empties)
  
• Determining XON/XOFF characters
  
• DTR Control mode (enable/disable/input handshaking)
  
• RTS Control mode (enable/disable/input handshaking/toggling on transmit)
  
• Output handshaking using CTS/DSR/DCD (control signal determines when to transmit)
  
• Input sensitivity using DSR (reception of data controlled by DSR)
  
• Error Replacement character and processing
  
• Break Replacement character and processing
  
• Null stripping
  
• Receive/Transmit Timeout processing
  
• Extended Hardware Buffering control

To maintain upward compatibility, it is the responsibility of the application to call ASYNC_GETDCBINFO before calling ASYNC_SETDCBINFO. The appropriate information in the returned control block should be modified by the application; then the Function 53h can be performed.

Note: The bit fields that are labeled reserved are returned as 0, but applications should not make this assumption or assume that the fourth bit combination will never be returned for DTR Control mode, Read Timeout processing, or Extended Hardware Buffering. Applications should not attempt to manipulate these reserved bits.