Quote Originally Posted by tumbleweed View Post
If you're using interrupts on either end then you shouldn't use SEROUT/SERIN as interrupts will upset the timing.
You should use the hardware HSEROUT/HSERIN routines, but then you will have to use the dedicated UART IO pins.

Also, you would be better off running the receiving end with a faster osc setting... try 32MHz instead of 16.
The PIC ports with HSEROUT and HSERIN are already taken. Using a baud rate of 9600 instead of 19200 made a difference. It is now working fine. The USB Darrel's interrupt takes micro seconds to execute. I measured it once. I forgot the exact number, but it was very small. That shouldn't affect the SEROUT/SERIN.