Post by thread:$-1 ??

$ is the address of the instruction the $ is in. This is an easy way of doing a loop to wait for something without having to do another label. For example... btfsc portb,0 goto $-1 will loop until RB0 is pulled low. Harold On Thu, 8 Apr 1999 23:49:09 +1000 Glen <spam_OUTelectmeTakeThisOuTTIG.COM.AU> writes: {Quote hidden}>hi , hope you can help. > >i've seen these a few times , but don't know what they mean >could someone please explain for me. > >$-1 >$+1 > >thanks >glen > ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]

Hi Glen. $ mean current PC address. > hi , hope you can help. i've seen these a few times , but don't > know what they mean could someone please explain for me. > $-1 loop1: nop ;some cmd... goto $-1 ;will jump to loop1 ;usually used for loops > $+1 goto $+1 ;will jump to loop2 loop2: ;usually used for 2clock delay (1word) ;instead of nop (1clock 1 word) nop ;some cmd... Common case: cmd1 ;1word cmd2 ;1word cmd3 ;1word goto x cmd4 ;1word cmd5 ;1word cmd6 ;1word x: --- $-3 will spend 2 clocks and jump to cmd1 $-2 ... to cmd2 $-1 ... to cmd3 $ ... to itself, endless loop , sometimes usefull ;-) $+1 ... to cmd4 $+2 ... to cmd5 $+3 ... to cmd6 and so on ... WBR Dmitry.

Glen wrote: > hi , hope you can help. > > i've seen these a few times , but don't know what they mean > could someone please explain for me. > > $-1 > $+1 > $ is program counter normal example movlw 0xFF movwf temp loop decfsz temp,f goto loop $ example movlw 0xFF movwf temp decfsz temp,f goto $ - 1 ; when counter gets here we tell counter to - 1 it will go one line above. using $ you save lots of labeling BUT you have to be careful about this it doesn't work every where. it happened to me a few times and I couldn't find the reason why replacing $ to label worked. Andre Abelian Andre > thanks > glen

>hi , hope you can help. > >i've seen these a few times , but don't know what they mean >could someone please explain for me. > >$-1 >$+1 Glen - the symbol '$' means 'current Program Counter address'. The value of $ is incremented at the END of the current instruction. The sequence '$-1' is the same as: Loop goto Loop In other words, loop forever. The sequence '$+1' is best considered to be a 2 cycle nop. It really means: goto Label Label Note that you can use integers other than 1 but you should limit that practice to jumps that are no longer than 2 or 3 locations. The following is generally considered acceptable: incfsz counter,F goto $+2 goto somehwere execute some code starting here This little fragment emulates an 'incfsnz' instruction - increment the counter and skip if NOT zero. You might use this if you didn't want the increment or test to affect the status register (otherwise you would just use the pair of instructions incf counter / skpnz). Hope this helps. dwayne Dwayne Reid <.....dwaynerKILLspam@spam@planet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (403) 489-3199 voice (403) 487-6397 fax Celebrating 15 years of Engineering Innovation (1984 - 1999) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. My posting messages to Usenet neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email.

Moments ago, I sent an explanation of how $-1 works to the list. It is wrong. I said: The sequence '$-1' is the same as: >Loop > goto Loop > >In other words, loop forever. This is WRONG. My appologies for the confusion. Not enough coffee yet this morning, I guess. dwayne Dwayne Reid <dwaynerKILLspamplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (403) 489-3199 voice (403) 487-6397 fax Celebrating 15 years of Engineering Innovation (1984 - 1999) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. My posting messages to Usenet neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email.

Dmitry Kiryashov wrote: {Quote hidden}> > Hi Glen. > > $ mean current PC address. > > > hi , hope you can help. i've seen these a few times , but don't > > know what they mean could someone please explain for me. > > > $-1 > > loop1: > nop ;some cmd... > goto $-1 ;will jump to loop1 > ;usually used for loops > > $+1 > > goto $+1 ;will jump to loop2 > loop2: ;usually used for 2clock delay (1word) > ;instead of nop (1clock 1 word) > nop ;some cmd... > > Common case: > > cmd1 ;1word > cmd2 ;1word > cmd3 ;1word > goto x > cmd4 ;1word > cmd5 ;1word > cmd6 ;1word > > x: > --- > $-3 will spend 2 clocks and jump to cmd1 > $-2 ... to cmd2 > $-1 ... to cmd3 > $ ... to itself, endless loop , sometimes usefull ;-) > $+1 ... to cmd4 > $+2 ... to cmd5 > $+3 ... to cmd6 > > and so on ... > > WBR Dmitry. PC=Program Counter

There are cases where you HAVE to use the $ notation. Try putting a label in a macro. The second time you use the macro the assembler will complain about duplicate labels. And I often use $+1 as a 2 cycle 1 word delay instead of using two NOP's (and therefore 1 more word of precious program space) to accomplish the same thing. My 2 cents worth. Adam Bryant (age 0x23) .....abryantKILLspam.....peaktech.com (work) EraseMEadamdbspam_OUTTakeThisOuTjuno.com (home) Parker, CO, USA Robotics, RC Airplanes, anything using a PIC On Thu, 8 Apr 1999 17:00:39 -0400 Ralph Stickley <rstickleyspam_OUTDATALUX.COM> writes: {Quote hidden}>Exactly why it should never, ever be used!!! Type the label! > >Your hard disk is not full, the extra assembly time is zero. Your >debug and >maintenance time is your most valuable asset, don't waste it trying to >keep this >outdated scheme in your code. > >Ralph > >Free advice is worth every penny!:-0 > > >Dwayne Reid wrote: >> >> Moments ago, I sent an explanation of how $-1 works to the list. It >is wrong. > ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]

On Thu, 8 Apr 1999, Dmitry Kiryashov wrote: > Hi Ralph. > > > Exactly why it should never, ever be used!!! Type the label! > > > > Your hard disk is not full, the extra assembly time is zero. > > Your debug and maintenance time is your most valuable asset, > > don't waste it trying to keep this outdated scheme in your code. > > It's very depends on ability thinking absolutly and relativly ;-) > Sometimes one is better, sometimes another... > > Hint: absolute and relocatable addressing also consider something like this: goto $+1 goto $+1 goto $+1 which is a 3-instruction 6-cycle delay. I find it much easier to read than labelled version goto L322 L322: goto L333 L333: goto L334 L334: preference, style ... BTW, Dwayne has made many useful contributions to the piclist. He's also posted an error before - but so has every regular poster. BFD. Scott

Scott Dattalo wrote: > <snip> > > > It's very depends on ability thinking absolutly and relativly ;-) > > Sometimes one is better, sometimes another... > > > > Hint: absolute and relocatable addressing > > also consider something like this: > > goto $+1 > goto $+1 > goto $+1 > > which is a 3-instruction 6-cycle delay. I find it much easier to read than > labelled version > > goto L322 > L322: goto L333 > L333: goto L334 > L334: > How about a macro: delay 6 ; wait for something to happen... Seems easier to read, and the details are hidden in the macro. If the number is larger that 'x' the macro may even implement a loop. In either case, I know what is meant by the code, maybe not exactly how it was implemented. Understanding what the code does is a lot of times separate from understanding how it is implemented. Granted, some code must be fully visible to indicate the timing or other implications associated with the code. Hidding such details in macros can sometimes lead to other errors. However, I tend to make such timing critical code highly commented to point this out. >From the $ notation, I only know that I must try to find the documentation on $ (where is this ?), understand how the PIC increments the PC and so on. The fact that this came up as a question indicates some sort of problem. Question: What do the following do ? ---- goto $+1 goto loop loop: ---- goto $-1 loop: goto loop ---- goto $ ???? ----- As with any 'concise' notation, this can be abused. Note that I also never use a lot of the notations in 'C' which must be 'interpreted' by the reader before the meaning of the code is understood. > preference, style ... > Yes, that is a good point. Style is often left out of the code when we move from high level language to assembler. This is obvious by many examples given in the app notes from Micro-chip. > BTW, Dwayne has made many useful contributions to the piclist. He's also > posted an error before - but so has every regular poster. BFD. > > Scott My apologies to Dwayne, I didn't not mean to jump on any specific error he may have made. I was only pointing out that this notation is error prone and, as a general guideline of (my?) style, should be avoided to prevent errors that can easily be prevented. We all make enough mistakes anyhow, I'm only suggesting to adopt a style that can help prevent as many as possible. Ralph

Check out the LOCAL keyword used by the pre-processor. >From the MPASM help file: "A local label is one that is defined with the LOCAL directive (see Chapter 3). These labels are particular to a given instance of the macro's instantiation. In other words, the symbols and labels that are declared as local are purged from the symbol table when the ENDM macro is encountered." This seems to work fine and I have used it often.... Ralph Adam Bryant wrote: > > There are cases where you HAVE to use the $ notation. Try putting a > label in a macro. The second time you use the macro the assembler will > complain about duplicate labels. And I often use $+1 as a 2 cycle 1 word > delay instead of using two NOP's (and therefore 1 more word of precious > program space) to accomplish the same thing. > <snip>

Hi Ralph. > Question: What do the following do ? > ---- > goto $+1 > > goto loop 2 clocks delay if tricks with pclath isn't used, usually cause jump to next address ;-) > loop: > ---- > goto $-1 > > loop: > goto loop usually used for waiting while some condition will occur, for instance testing of some bit. btfss(c) some_bit_somewhere goto $-1 As only condition will postive next program will start executing. If PCLATH is set to another page will cause switching to another program page. > goto $ Either to lock code while expecting some interrupting event or jump to another program page (PCLATH is set properly) WBR Dmitry.

Good point (says he after realizing he engaged mouth before brain, AGAIN!) I had seen the reference to the LOCAL directive, but skipped over it and have not gotten in the habit of using it. I also have a problem with coming up with very creative label names anyway, and therefore use the $ references instead of my usual creative labels that usually end up looking like Loop1:, Loop1a:, Loop1b: Certainly when I do larger programs or any programs that will be looked at by someone else, I try to minimize the use of $ and maximize the descriptiveness of my labels. But as with anything, there are cases where the use of $ has its advantages. Adam Bryant (age 0x23) @spam@abryantKILLspampeaktech.com (work) KILLspamadamdbKILLspamjuno.com (home) Parker, CO, USA Robotics, RC Airplanes, anything using a PIC On Fri, 9 Apr 1999 09:37:56 -0400 Ralph Stickley <RemoveMErstickleyTakeThisOuTDATALUX.COM> writes: {Quote hidden}>Check out the LOCAL keyword used by the pre-processor. >>From the MPASM help file: > >"A local label is one that is defined with the LOCAL directive (see >Chapter 3). These labels are particular to a given instance of the >macro's instantiation. In other words, the symbols and labels that >are declared as local are purged from the symbol table when the ENDM >macro is encountered." > >This seems to work fine and I have used it often.... > >Ralph > >Adam Bryant wrote: >> >> There are cases where you HAVE to use the $ notation. Try putting a >> label in a macro. The second time you use the macro the assembler >will >> complain about duplicate labels. And I often use $+1 as a 2 cycle 1 >word >> delay instead of using two NOP's (and therefore 1 more word of >precious >> program space) to accomplish the same thing. >> ><snip> > ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]

Gerhard Fiedler wrote: >> goto $-1 >> >>loop: >> goto loop > >these are not the same. the $ points to the current instruction, so >would be > > loop: > <some instruction> > goto loop Hi there, Gerhard. That was my mistake, not Ralph's. I noticed the error right after I uploaded the message and sent a retraction. Sorry about the confusion on my part. dwayne Dwayne Reid <spamBeGonedwaynerspamBeGoneplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 15 years of Engineering Innovation (1984 - 1999) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. My posting messages to Usenet neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email.