This may help somebody. The MCB2130 board uses a couple of pins on the com0 interface to generate a reset or interrupt. I thought I was ok to leave these unconnected when using the serial port for other purposes. However, stray capacitance in the cable was causing crosstalk, making the board reset itself - but only above 9600 baud. Grounding the unused pins (4 and 7) fixed the problem. Maybe a board revison could add some resistors from the base of T1 and T2 to ground. Dave