How do I find out if an unusual baud rate is supported by my Brainboxes Serial card?


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The baud rate which can be obtained from a card using Brain Boxes Serial Solutions drivers depends upon the type of card and in which OS it is used. For standard cards which operate up to 115200 baud The baud rates supported by the card for the drivers Win9x, NT4, Win2K can be found by taking the maximum baud rate and dividing it by the required baud rate.

If the result is an integer value i.e. 115200/9600= 12 (say) then this baud rate is supported.

For Velocity cards which operate up to 921600 baud

For NT4 and Win2K the same applies as above but this time the maximum baud rate is 921600. i.e. 921600/61440= 15 is supported by both these OS. However this does not apply to win9x mainly for historical reasons.

The maximum baud rate for Win9x is 115200 baud and we can see 115200/61440 = 1.875 is not supported.

However 115200/57600= 2 is supported. (Please see note below about radio buttons)

For PCI RS422/485 15M and 18M Ultra velocity cards

For this we use the attached baud rate calculator program. Select which card is to be used and input the required baud rate. If the requested value is within 1% of the value the driver can provide, then an exact baud rate is displayed. If the driver cannot support this baud rate then the next highest or lowest baud rate is displayed.

Additional Information

All velocity cards which use the Win9x driver can access higher baud rates by using radio buttons found in device manager/multifunction adapter or device manager/ports/velocity port. Baud rates such as 57600 can be multiplied by 2,4 or 8. to give 115200,230400 or 460800 baud (say).

All drivers output the required baud rate if it is within 1% of that which can be calculated from the above. It must be remembered that the UART resynchronises at the start bit of each character, so can tolerate at least this degree of error. In theory, the maximum divisor value (the number obtained by dividing the required baud rate into the maximum baud rate) is 65536. In practice, the baud rate obtained is so slow, that the driver assumes a minimum of 300 baud.

PCMCIA cards follow the rule for velocity cards EXCEPT if using WinNT 4.0. The rule for standard card types is then applicable. The Baud Rate Calculator is available at the top of this page, and is also included on the Serial Solutions CD. The value of the crystal oscillator is required in order to use the calculator and this is entered into the crystal frequency field (full value, no decimal points). The desired baud rate is then entered and the calculator displays whether it is an exact match or whatever is the closest possible match.