piclist 1995\11\10\130911a >
Thread: PIC16C84 & PortB interrupt
face BY : Conny Andersson email (remove spam text)

At 10.36 1995-11-10 +0100, Philippe wrote:

>  PortB can generate INTERRUPT when there is change on RB.4..7, the
>documentation said: these pins are sampled on the Q1 cycle of read.
>The new input is compared with old latched value in every instruction cycle.
>HOW IT IS possible an interrupt occurs if portB is latched only on a READ
>instruction ?

Easy! The pins are sampled AND put in the portB register by the
MOVF/SWAPF/... instructions BUT they are also "sampled" by the interrupt
logic - two separate sample-circuits. The actual data on the pins are not
nescessarily the same as the actual data in the register.

-- Conny

See also: www.piclist.com/techref/microchip/ints.htm?key=interrupt
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