The Bit Rate field is a binary
integer representing the actual bit rate (bits-per-second) that the physical
device driver uses to set the bit rate of the COM device. For a COM port
that is supported by Enhanced UART or compatible serial communication devices,
the range is 10 bps - 345600 bps. The user can get the minimum and maximum
bit rates supported by the physical device driver on a COM port by using
"Function 63h - Extended Query Bit Rate".
Note:
Due to system overhead and the physical limits on the hardware cables, actual
bit rates might be restricted.
When this function is used for a COM port that has no support of the Enhanced
UART or compatibles, then the bit range supported by the device driver is
from 2 bps - 19200 bps. A call with a bit rate out of range fails with
the ERROR_INVALID_PARAMETER return code.