Hi,

Here I am analysing the problems which I find while studying the code which will result in not getting the desired speed.

The main problem is you are not restricting R4 in between 0 to 6.because you assign the speed only from 0 to 6 of R4.Then how will it work for another value.

So first restrict the value of R4.

The other reason is you write clause for r4 = 3,r4 = 5,r4 = 6 in increment button & r4 = 0,r4 = 1 & r4 = 2 in decrement button.But when you increment the r4 from 3 to 6 and now press decrement then the value of r4 = 5.So the speed for r4 = 5 would also reflects in decrement routine too.same way r4 = 0,r4= 1 sholud also reflects in increment too.

See the following code of delay

NOR_DEL:
        MOV R0,#0FFH
m1:
        MOV R1,#0FFH 
INLOP:
        MOV R2,#01H
m2:     DJNZ R2,m2
        DJNZ R1,INLOP
        DJNZ R0,m1
        RET 

In this code the value of speed loaded as r0,#0ffh.So your speed,you decide by pressing inc. & dec,. button will become null & void after furnishing one time only & then
it will work on the original speed.For avoiding these situatioan you should use register for that.

Your code shoude be

NOR_DEL:
        MOV R0,dly1
m1:
        MOV R1,dly2
INLOP:
        MOV R2,#01H
m2:     DJNZ R2,m2
        DJNZ R1,INLOP
        DJNZ R0,m1
        RET 

define dly1 & dly2 in the beggining & load the value in dly1 & dly2 while pressing the Increment & decrement button.

Your processor would become also hang because of the following code

NXT5: 	CJNE R4,#00H, NXT5 
        MOV R0,#0FFH                            ;Speed--- 
        AJMP NXT5 

if R4 is not equl to zero while you press decrment the down key the controller stuck on NXT5: label.isn't the case ?


So first consider all these points in this code for getting the desired speed.

Regards
Maunik