a delay - an explanation needed

delay




My two questions are

What does " $ +2 " mean"?

and take delay 250 ms for an example

how these codes make the delay 250ms delay?

Please explain it to me

Thanks a lot

Re: delay

Hi,

The $+2 means goto plus 2 Bytes of program memory, in the case of a 16F chip that is normally 2 instructions - while this may seem a handy shortcut to using a goto and label, if you move your code to other pics like the 18F then the same thing will only move it forward 1 instruction.

The code you posted is a little incomplete, what processor and what osc frequency are you using at it is the frequency/4 = clock cycle, that determines the delay period .

Also you are using 'goto' to get the delays routine and then 'retlw' - use 'call'

Try running your code with breakpoints and Simulators Stop watch at 4meg gives the results shown in the pic.

Re: delay

Thank you so much. It helped!

Re: delay

Hi,

Have you been able to see how it creates the delay ?

The osc frequency/4 gives the clock frequency or clock cycle that runs the micro.
If you look at the datasheet Instruction Set Summary, the 2nd page that shows a list of all of them, there is a column labelled ' cycles' ie the number of 'clock cylces' to execute an instruction.
If you are using a 4meg osc, then thats 4meg/4= a 1 meg clock cycle or .000,001 of a second = 1micro second per instruction ( well most instructions )

Your delay routine is just two loops of instructions use to create the required delay period.

As you can see the Sim Stop watch gives the delay time acheived and the number of intructions executed ( ie the delay loop ) to acheive this.

Have you been able to run the Sim ? it might seem a bit complicated to start with but its a handy tool to let you see what is going on at the single instruction rate - you can also view how all the system and user registers are being changed as your code runs though.

Re: delay

Hi,

I am able to run it, but I seldom use those fuctions.

it will take me some time to get used to it.
If I have further qs, I will surely ask away.

Thank you so much for being so helpful.