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Multiplexer Driver Developer’s Guide 
2.4 Handling of Control Lines on Virtual Ports
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Mux_Drv_DevGuide_v07
Page 14 of 36
2006-9-27
Confidential / Released
2.4
Handling of Control Lines on Virtual Ports
Summary of control line handling.
2.5
Limitation of Virtual Ports
Flow control can be set to RTS/CTS or DSR/DTR. XON/XOFF flow control is not supported. Hardware flow con-
trol on the virtual COM ports is handled internally by the Multiplexer Protocol.
The WinMux2k driver handles neither modem nor serenum IO-control requests. 
The WinMux2k driver supports only 8 data bits, no parity, and one stop bit. 
The function IOCTL_SERIAL_XOFF_COUNTER is not supported.
The following functions return “success”, but have no effect at all:
IOCTL_SERIAL_SET_BREAK_ON
IOCTL_SERIAL_SET_BREAK_OFF
IOCTL_SERIAL_SET_XOFF
IOCTL_SERIAL_SET_XON
IOCTL_SERIAL_RESET_DEVICE 
Virtual ports accept any baud rate, though the changed setting will be ignored. Calling the function Open() to a
virtual port can take up to 40 seconds. It fails if the module is not connected.
Table 2:  Virtual serial port with Multiplexer Protocol version 2
Signal
Description
RING
Read from hardware port, distributed to the first virtual port
DCD
Read from hardware port, distributed to the first virtual port
DSR
Received with Modem Status Command
DTR
Set by user, sent with Modem Status Command, initialized with 1
CTS
Received with Modem Status Command
RTS
Set by user, sent with Modem Status Command, initialized with 1
Table 3:  Virtual serial port with Multiplexer Protocol version 3
Signal
Description
RING
Received with Modem Status Command
DCD
Received with Modem Status Command
DSR
Received with Modem Status Command
DTR
Set by user, sent with Modem Status Command, initialized with 1
CTS
Received with Modem Status Command
RTS
Set by user, Send with Modem Status Command, initialized with 1