Hello everyone 'Good Morning' Its Morning here

These are the codes generated from a delay generator website.

I am interested in knowing $? and $+2? What does it mean?

If this is simple question don't flare at me point me to good website so I can read more about PIC.

Learning PIC is more fun than writing reports Just a side comment

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Hesham Ismail Mohammed Sharif
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$ is assembly for the current program counter value. It points to the next instruction to be executed so if the next instruction takes 2 bytes "goto $+2" skips the next instruction

 

Thanks for replying

Can You explain more?

I understand that d1 is loaded with a value of 0x11 which is 17 decimal.

decrease 1 from it, it will be 16 right. Then goto $+2? This line confuses me?

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Hesham Ismail Mohammed Sharif
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You'll find the older 16F have a few quirks that are gone in the 18F
Wait till you hit the RMW bug. The good news is the new 14bit core fixes the quirks of the older 14bit core. Also seems the older 33 instruction core is at the end of development in favor of the updated 44 instruction core.

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Bill
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A good way to understand what is going on is to run the simulator in MPLAB. You can single step and watch the registers change. There is also a stopwatch so that you can see how long loops take.

 

Hi,

goto $

is go to the current program location, which is also the same as:

Label
goto Label

while goto $+2, it can be said go to the next two program location. So:

is also the same as:

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bananasiong

 

Do you think, it should look like this

Or Am I wrong?

I understand goto $ very well explained when you explained goto $+2 I was lost.

BTW, I am interested in activating stopwatch in simulation any idea what to do or press?

Sorry for my Newbie questions!!

Thanks in advance

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Hesham Ismail Mohammed Sharif
Thank me if you want

 

No, it should not look like that. You are wrong!

In this code:
goto $+2 means move the program counter from the current program memory location to current memory location + 2. So PC + 1 = decfsz d2,f. And PC + 2 = the next goto $+2. That means it skips right to the bottom every time until that variable finishes counting down and becomes zero.

Have a look at Figure 13-1 on page 103

Each instruction takes 14 bits. Each time the program counter increments, it moves 14-bits higher in memory (to the next instruction).

Goto $+1 means move the PC (Program Counter) from the current position to the current position + 1 (increment it). In other words it just goto's to the next instruction. Pointless of course, since it was going there anyway.

Goto $+2 means move the PC two instructions ahead, skipping the next instruction. You can do the same thing with a label, but for little short skips like that, why bother? It's obvious (not to you yet, but you'll get it. ) what you're doing.

Clear as mud, right?

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Futz's Microcontrollers & Robotics
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The OP was lost because he sees "GOTO $+2" meaning GOTO$ first, then adds 2 to the value of whatever variable.

Of course it should be GOTO(current address+2).

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L.Chung

 

what is f? how is it 1?

 

The instruction is: decrement the value in 'd1' register and place the result back into 'd1' .
The 'f' is the part of the instruction which tells the program where put the result of the decrement.
If the Instruction was decfsz d1, W it would decrement 'd1' and put the result in 'W', the working register.

OK.

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Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

I thought this instruction says ‘Decrement the register (in this case d1) by the number that follows the comma.

 

I thought this instruction says ‘Decrement the register (in this case d1) by the number that follows the comma.

 

No, the decfsz d1,f and other 'dec's always change the contents of d1 reg by '1'.
Likewise a incf d1,f would always increment the contents of d1 reg by '1'.

If you wanted to change the contents of d1 reg by more than '1' you could use
add or sub intructions.

EDIT:
All of these instructions are on the PIC datasheet

Attached Thumbnails

 

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Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/