The Option Register

The OPTION register is a readable and writable register which contains various control bits to configure the TMR0/WDT prescaler, the external INT interrupt, TMR0, and the weak pull-ups on PORTB.

Bits 0, 1 and 2 are the three prescaler division ratio bits for either the timer/counter module or the watchdog timer WDT, depending on which of these have been allocated for use.

Bit 3 selects the assignment of the prescaler/postscaler to either the timer/counter, or the watchdog timer.

Bit 4 selects whether the timer/counter increments on the falling edge or the rising edge of the external square wave signal on pin TOCKI when external timer clocking is selected; otherwise, the waveform is ignored.

Bit 5 is used to choose between external timer clocking via the TOCKI pin, or via the internal instruction cycle clock.

Bit 6 selects between interrupt triggering on either a rising or falling edge.

Bit 7 enables or disables the weak internal pull-ups on the pins of PORTB when the port is configured as an input. The pull-ups are disabled when the port is in output mode.