The Bit Rate field is a binary
integer representing the actual bit rate (bits-per-second) that the physical
driver uses to set the bit rate of the COM device. For bit rates up to
19200 bps, the physical device driver sets the rate only if the hardware
can support the rate within .01% margin of error. The exceptions are for
110 and 2000 bps, which can have an error of up to .026% and .69%, respectively.
In all other cases, if the requested rate cannot be achieved by the hardware
within .01% tolerance, the IOCtl fails with an ERROR_INVALID_PARAMETER return
code.
For bit rates beyond 19200 bps, the physical device driver does not check
the .01% margin of error. It is the user's responsibility to maintain the
bit rate tolerance. After calling Function 41h to set a bit rate higher
than 19200 bps, the user calls "Function 61h - Query Bit Rate" to check
the actual bit rate set on a COM port.
The recommended bit rate values are:
- 110
- 150
- 300
- 600
- 1200
- 1800
- 2000
- 2400
- 3600
- 4800
- 7200
- 9600
- 19200
- 38400
- 57600
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