Two statements from assembly - trying to convert the code in PBasic Pro

[Megahertz]

Can someone please advise what the following two statements mean (or doing) in the code? I have the code in assembly which I am converting to basic pro, but I don't have a clue what these statements are doing. They are extracted from the ISR routine.

        
movlw   ((INTHAND) >> 8)
movwf   PCLATH

[SteveB]

movlw ((INTHAND) >> 8) => Shift the constant (literal) 8 bits right (equivalent to dividing by 256) then put the value in WREG

movwf PCLATH => Move the value in WREG into PCLATH.

So, these two statement combined are putting INTHAND/256 into the the middle byte of the program counter.

[Megahertz]

Steve, but
1)INTHAND is not a variable, in fact it is mentioned in the statement

define      INTHAND     _ISR

2)What is the basic purpose of loading value in PCLATH

cheers

[SteveB]

Steve, but
1)INTHAND is not a variable, in fact it is mentioned in the statement

define      INTHAND     _ISR

Yes, you are right. But I didn't say it was a variable.

2)What is the basic purpose of loading value in PCLATH

The PCLATH is used (along with PCLATU) to make changes to the Program Counter, which is akin to directing the the program to a new location in the code: a "Computed GOTO."

[Megahertz]

I am confused, you said

Shift the constant (literal) 8 bits right (equivalent to dividing by 256) then put the value in WREG

Where is the constant here?

[HenrikOlsson]

I really suck at assembly programming but I'm going to say (write) what I think, then hopefully someone will correct me if I'm wrong.

The constant in this case is called INTHAND which is defined to contain the adress, in program memory, where the routine _ISR is located. What happens is that PCLATH (the high byte of the program counter) gets loaded with the 8 high bits of the adress of _ISR. I suspect there's also code to take the low 8 bits and put them in PCLATU. All in all, that would cause the program to jump to _ISR.

After reading SteveB's other posts that's my understanding of it but again I might very well be wrong.

/Henrik.