Scampy, I have had problems using DEBUG with REAL interrupts in the past as DEBUG is a software serial routine. I would imagine that the HSEROUT and HSERIN routines would have the same problem. I realize that HSERIN and HSEROUT use the hardware for the serial buffering but, the calls for either may give you grief. I have only used the interrupt routines with PIC's that have 2 serial ports in the past without any problems @ 38400 baud. I do have 1 application that I use both serial ports and DEBUG with in the same program. There I have to shut off both interrupt driven serial ports to reliably use the DEBUG port. I don't know about using the HSEROUT or HSERIN routines? Hope this helps....