C# RS232 connection

I have a serial connection in C#compact framework, on a PDA, with a device running embedded C. My problem is that if the owner of the C code puts interrupts in, I receive data. Without the interrupts the transfer seems to be too fast. The interupts are an un acceptable solution. We are both connecting at 19200 baud. We are using bare bones connection, a 9-pin cable, and no flow control. Does anyone have any suggestions? Thanks in advance for any and all help.