16f vs 18f

P

pixman

Member

• Feb 17, 2015

• #1

I would like to know if the instruction BTFSS 3,0 is executed in the same way for 16f and 18f PICS.

 

Ian Rogers

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Most Helpful Member

• Feb 17, 2015

• #2

BTFSS 3,0 is accessing the status bit on a pic16

The status register on a pic18 is high, 0xFD8 on a pic18f252.... BTFSS 3,0 on a pic18 will be access ram!

So The answer is No!!

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• Feb 17, 2015

• #3

Fairly obviously you should NEVER be using 'BTFSS 3,0', utterly pointless, confusing, and non-portable - use the correct mnemonics as you're supposed to (which makes the code 'portable-ish' as well.

 

P

pixman

Member

• Feb 17, 2015

• #4

Hi Nigel

It comes from your Tutorial 11.1 which converts the NumL and NumH to decimal.
Lb1:
addwf Ones,f
decf Tens,f
btfss 3,0
goto Lb1

How would you change this to work.

 

granddad

Well-Known Member

Most Helpful Member

• Feb 17, 2015

• #5

I coded as BTFSS STATUS,Z ; or C etc. ( always used uppercase for some reason ...)
<3 asm.

 

P

pixman

Member

• Feb 17, 2015

• #6

Tried all STATUS BITS Z, C ,DC, OV ,N , Non work.

 

Ian Rogers

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• Feb 17, 2015

• #7

Yeah Nigel!!!

(I hate when that happens )... LOL

 

Ian Rogers

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• Feb 17, 2015

• #8

PIC18's have branch instructions... BNC, BNN, BNZ etc...

When using Pic18 try this " BTFSS STATUS,C,0 " The command defaults to Access ram "0" SFR's and Access ram have bit access

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• Feb 17, 2015

• #9

pixman said:

Hi Nigel

It comes from your Tutorial 11.1 which converts the NumL and NumH to decimal.
Lb1:
addwf Ones,f
decf Tens,f
btfss 3,0
goto Lb1

How would you change this to work.

Click to expand...

As the comments in the code explain, that routine was downloaded from the PICList

I'm pretty sure I've got a version somewhere that I converted for the 18F series though?, I'll see if I can find it tonight.

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• Feb 17, 2015

• #10

OK, took a bit of finding (as it was 2008), but here's TUT3.3 for an 18F2550 - the offending line was simply replaced by BTFSS STATUS, 0 - although it should really be BTFSS STATUS, C

 

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P

pixman

Member

• Feb 18, 2015

• #11

I got it sorted out after a battle. I used the BTFSS STATUS,C but it would not register the overflow at the correct time.
The decf also affects the overflow bit C. So I swopped the addwf and decf around and its working now.

Lb1:
decf Tens,f
addwf Ones,f
btfss STATUS,0
goto Lb1

 

Jon Wilder

Active Member

• Feb 23, 2015

• #12

Nice that they have branch instructions. However, nothing beats having a compare, jump if not equal (cjne) like a good ol' 8051.

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• Feb 23, 2015

• #13

Jon Wilder said:

Nice that they have branch instructions. However, nothing beats having a compare, jump if not equal (cjne) like a good ol' 8051.

Click to expand...

That's not a RISC processor though