If a general failure error is not returned, the physical device driver performs the action described in the Bit Rate field. An OPEN request packet does not cause the physical device driver to change the bit rate from its previous value. The initial value is 1200 bps.

The COM device hardware determines which bit rates can be supported on a given system. The range of bit rates supported by Function 41h is 2 bps to 19200 bps for COM ports on conventional serial devices. For COM ports on enhanced serial devices, the range is 10 bps to 57600 bps. A call with a value beyond this range fails with the ERROR_INVALID_PARAMETER return code.