## Physical Device Driver Reference

[prev][next][parent][TOC]

### ASYNC_SETBAUDRATE (41h) - Bit Rate

Bit Rate 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