Not all Mac serial ports are capable of thise speed, but for those that are, it's a simple CONTROL call. See Inside Macintosh: Serial Manager for details.
OK thanks for that, I've had a look and am still have trouble, ho hum !
I'm calling the FN CONTROL like this,
DIM pbBlk.50
pbBlk.ioRefNum% = -6 (Modem port)
pbBlk.csCode% = 13 (set new baud rate)
pbBlk.csParam& = 115200 (baud rate I want to set)
osErr% = FN CONTROL (@pbBlk)
Now Inside Mac says that after FN CONTROL it will return the baud rate that has been set in pbBlk.csParam, I'm checking this by,
BaudRate& = PEEK LONG(@pbBlk.csParam&)
However on baud rates from 300 up to 19200 there is not problem. But above that pbBlk.csParam returns gibberish. I'm testing this on a PPC 4400 which I know can run 115200.