The PIC16F1939-I/PT is a 8-bit 40-pin Microcontroller with LCD driver featuring nanoWatt XLP technology. This device has a hardware stack memory 15-bit wide and 16 words deep. A stack overflow or underflow will set the appropriate bit (STKOVF or STKUNF) in the PCON register and if enabled will cause a software reset. There are two 16-bit file select registers (FSR). FSRs can access all file registers and program memory, which allows one data pointer for all memory. When an FSR points to program memory, there is one additional instruction cycle in instructions using INDF allows the data to be fetched.