Post by thread:Code question

I am basically new to Pic`s and I am having trouble understanding a line in some code I came across. Any help would be appreciated. Below is the code: movlw 0D0 btfss portc,w --Is this line checking for a specific bit, and if so which one? Dominic

portc,w-- w is replaced with a 0 when assembled. ---------- > From: Dominic Gualtieri <spam_OUTdgualtieriTakeThisOuTNETWORX.ON.CA> > To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Subject: Code question > Date: Thursday, May 21, 1998 3:59 PM > > I am basically new to Pic`s and I am having trouble understanding a > line in some code I > came across. Any help would be appreciated. Below is the code: > > movlw 0D0 > btfss portc,w --Is this line checking for a specific bit, and > if so which one? > > Dominic

Dominic Gualtieri <PICLISTKILLspamMITVMA.MIT.EDU> wrote: > I am basically new to Pic`s and I am having trouble understanding a > line in some code I came across. Any help would be appreciated. > Below is the code: > > movlw 0D0 > btfss portc,w --Is this line checking for a specific bit, > and if so which one? Dominic: The author of this code was also new to PICs... Or he was going to a lot of trouble to make his code difficult to understand. The code assembles without errors only because of a convenient accident: Internally, MPASM defines "W" as equivalent to "0" so instructions like "MOVF REG,W" will assemble correctly. Because MPASM treats "W" as "0", the BTFSS line is assembled as "BTFSS PORTC,0"... So it's checking bit 0 of the "PORTC" register. I'd be real surprised if that's what the code's author intended, though. -Andy === Andrew Warren - .....fastfwdKILLspam.....ix.netcom.com === Fast Forward Engineering - Vista, California === http://www.geocities.com/SiliconValley/2499 (personal) === http://www.netcom.com/~fastfwd (business)

On Thu, May 21, 1998 at 06:55:15PM -0800, Andrew Warren wrote: > Because MPASM treats "W" as "0", the BTFSS line is assembled as > "BTFSS PORTC,0"... So it's checking bit 0 of the "PORTC" register. > > I'd be real surprised if that's what the code's author intended, I suspect that at some time the author decided that writing things like addwf x,0 was a Bad Idea because it isn't obvious where the destination is, so decided to do a global replace of ,0 with ,w - and caught a few other things in the net. Clyde -- Clyde Smith-Stubbs | HI-TECH Software Email: EraseMEclydespam_OUTTakeThisOuThtsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger clydespam_OUThtsoft.com | AUS: +61 7 3354 2411 +61 7 3354 2422 --------------------------------------------------------------------------- HI-TECH C: compiling the real world.

---Dominic Gualtieri <@spam@dgualtieriKILLspamNETWORX.ON.CA> wrote: > > I am basically new to Pic`s and I am having trouble understanding a > line in some code I > came across. Any help would be appreciated. Below is the code: > > movlw 0D0 ? > btfss portc,w --Is this line checking for a specific bit, and > if so which one? BTFSS f, b - Bit Test f, Skip if Set b = 3-bit bit address f = 7-bit file register address > > Dominic > _________________________________________________________ DO YOU YAHOO!? Get your free @yahoo.com address at http://mail.yahoo.com

Dominic Gualtieri wrote: > I am basically new to Pic`s and I am having trouble understanding a > line in some code I > came across. Any help would be appreciated. Below is the code: > > movlw 0D0 > hex value is not right it should be 0xD0 or D0H or H'D0'this line means load hex D0 in W register > btfss portc,w --Is this line checking for a specific bit, and > this line is wrong but it will work becouse of w = 0same as btfss portc,0 you are testing bit 0 on portc it will skip if it is clear > if so which one? > > Dominic Andre