Help me compare two register values in 89C51

[vijaya_narayana]

guys i need your help i need to compare two register values and if it is equal the code must proceed to next sequence for this
i tried the following statement it gives error

CJNE A,R1,NEXT

is there any alternaste for this the data stored in a will be a floating value it is not a fixed value

the controller is 89c51

 

[IanP]

Re: help on 8051

First of all, you can't compare A and R1, but you can compare A with "location" 01h (which in fact is the address of R1) ..
Second, the result (equal) of the CJNE instruction is just "below" it, so:

CJNE A, 01h, Not_Equal
LJMP NEXT ; Here A is equal to 01h(R1) ..

Not_Equal: .. here you will continue if A is not equal to 01h(R1) ..

Regards,
IanP

 

[vijaya_narayana]

Re: help on 8051

thanks it is working fine

 

[hbaocr]

help on 8051

hi,
more than it...
If A<R1 the flag bit C =1
else A>=R1 the flag bit C =0
This function can be used for comparing two number by tesing bit C we can know which number is more than

 

[wek]

Re: help on 8051

First of all, you can't compare A and R1, but you can compare A with "location" 01h (which in fact is the address of R1) ..

... but of course only if register bank 0 is active (which is the default case)...

Sounds like hairsplitting, but may save some problem hunting later if the OP decides to implement bank switching. The proper way to assign the absolute address in some of the assemblers is to use the builtin AR0..AR7 symbols together with the USING directive.

If bank-independent solution is needed, there are two options: either to move Ri to a direct-addressed location before the compare (often, B is used for this task; but any other location suffices); or, if content of A (and C) may be destroyed, use subb (or xrl, if only equality test is required).

JW