|
Hi, PIC18 and MPASM: what is the thing about W and WREG ? Are those labels not 100% compatible? The following lines: SUBWF MCI,WREG SUBWF LIMSTAT,WREG ANDWF LIMPSTORE,WREG all generate the compiler warning "Argument out of range. Least significant bits used." But the following lines generates no warnings: SUBWF MCI,W SUBWF LIMSTAT,W ANDWF LIMPSTORE,W I thought W and WREG interchangeable ....so what's the difference between 'em? -- ******************************************* VISIT MY HOME PAGE: <http://home.online.no/~eikarlse/index.htm> LAST UPDATED: 23/08/2003 ******************************************* Best Regards Eirik Karlsen |
|
|
W and WREG
Started by ●February 7, 2004
Reply by ●February 7, 20042004-02-07
|
Don't know. W and WREG must be defined somewhere. Normally in the .inc file. The ones I looked at only define W, and define it as H'0000'. I think WREG must be defined for you somewhere as a larger than 8 bit value to give that error. As long as the constant evaluates to zero any label should work. Chad --- Eirik Karlsen <> wrote: > Hi, > PIC18 and MPASM: > what is the thing about W and WREG ? Are those labels not 100% > compatible? > > The following lines: > SUBWF MCI,WREG > SUBWF LIMSTAT,WREG > ANDWF LIMPSTORE,WREG > all generate the compiler warning "Argument out of range. Least > significant bits used." > > But the following lines generates no warnings: > SUBWF MCI,W > SUBWF LIMSTAT,W > ANDWF LIMPSTORE,W > I thought W and WREG interchangeable ....so what's the difference > between 'em? > -- > ******************************************* > VISIT MY HOME PAGE: > <http://home.online.no/~eikarlse/index.htm> > LAST UPDATED: 23/08/2003 > ******************************************* > Best Regards > Eirik Karlsen > ===== My software has no bugs. Only undocumented features. __________________________________ |
Reply by ●February 7, 20042004-02-07
|
Hi Eirik,
WREG represents the 8-bit W register (the
accumulator). W is an equate (alias) for a singe bit value of 0 and F is an
equate (alias) for a single bit value of 1. W and F are used by certain
instructions that operate on both the W register and another register to control
whether the result is stored in the W registor or the other register. For
example the encoding for
ANDWF f, d
is 00 0101 d fff ffff
This ANDs the W register with register
'f'' If 'd' is 0 the result is stored in the W
register. If 'd' is 1 the result is stored back in register
'f'.
The use of ,W or ,F is just to make the code
more readable. You could writer ANDWF REG1, W also as ANDWF REF1, 0
You get the "argument out of range" error
because in the 17F and 18F parts, the accumulator is at address $0A and
Microchip's include files have the following:
WREG equ 0Ah
so when you write
SUBWF MCI, WREG
your really writing
SUBWF MCI,
0Ah
0Ah in binary is 00001010. Since the assembler
truncates to the LSB and that is 0 in this case, its the same as writing
SUBWF MCI, 0 or SUBWF
MCI, W
so the net affect is what you wanted in the
first place, albeit with the warning message. Better to be safe than sorry
though so use W or F
Scott Kellish
SoftSystem Solutions
s...@comcast.net
|
Reply by ●February 7, 20042004-02-07
|
----- Original Message ----- From: Eirik Karlsen <> To: <> Sent: Saturday, February 07, 2004 6:44 PM Subject: [piclist] W and WREG > Hi, > PIC18 and MPASM: > what is the thing about W and WREG ? Are those labels not 100% compatible? > > The following lines: > SUBWF MCI,WREG > SUBWF LIMSTAT,WREG > ANDWF LIMPSTORE,WREG > all generate the compiler warning "Argument out of range. Least significant bits used." > > But the following lines generates no warnings: > SUBWF MCI,W > SUBWF LIMSTAT,W > ANDWF LIMPSTORE,W > I thought W and WREG interchangeable ....so what's the difference between 'em? I haven't used the 18 series but from what I've read the W register is mapped to a special function register as WREG. It allows you to perform register only operations on W as though it were a RAM location e.g. BTFSS WREG,3 or RRF WREG I looked this up in the 18 series docs and WREG is at address $FE8 Doing ADDWF COUNT,WREG would be like doing ADDWF COUNT,FRED i.e. trying to add two registers together Regards Sergio Masci http://www.xcprod.com/titan/XCSB - optimising structured PIC BASIC compiler |
Reply by ●February 7, 20042004-02-07
|
Sorry,
WREG is in different locations in the 17F and
18F parts. Its at 0Ah in the 17F parts and FE8h in the 18F parts. Either way,
the LSB is still 0
Scott
|
