Digital Electronics - The 8051 Microcontroller - Discussion

READ: MOV A,P1; Copy the P1 content into the accumulator (A=P1).

ANL A,#2H; do logic AND between accumulator (A) and an immediate data 02h (00000010b), and it will force the content of the accumulator to be 02h.

CJNE A,#02H, READ; if A is not equal to 02 ( in this case A will be 02h) then jump to a statement labelled as READ.

MOV P3,#FFH; fill an immediate data FFh into the P3.
NB.

This program will always go to the statement MOV P3,#0FFH without taking into account the content read from P1 into the accumulator.

1st : Copied to accumulator
2nd :ANDing operation
3rd : Compare jump if not equal
its always not equal
4th : Copied to port3 instruction

Thanks abhi.

Contents of Port1 should be mentioned clearly, so that we can perform or take decision on CJNE instruction rite !

@Imtiyaz, they have asked to check the 2nd lsb i.e 2nd bit right why you want to know the whole digit.

In the operand of CJNE, there is a address or data? please reply.

Line1. A = P1 'Read P1 then save in Acc.
Line2. A = A and 00000010 'And Operation.
Line3. If A <> 00000010 Goto Line1 'Compare.
Line4 Else P3 = #0ffh 'Send ffh to port 3.

@Ruben its correct by masking all bits except 2nd bit and checking whether second bit is high or low and jumping actions are taken.

Line 1: We will move the content of P1 to accumulator.

Line2: Why to AND with 2H please reply, they have asked to find whether second bit is high, so what's the necessary of adding here.

But what is the necessary of adding it with 2H, please answer me?