Post by thread:[pic]: beginning assembly question

> what are these equate statements doing? > > Is this assigning the var labels to positions in > memory or > setting aside memory space, or what? > > ; VARIABLE DECLARATION > > TEMPW EQU 0x20 Yes. This is assigning a label to an address in memory. This allows you to write your code as movf TEMPW,W ;load W with contents of address 20 instead of the more cumbersome movf 0x20,W or assigning a value to a label movlw TEMPW ;load W register with value assigned to TEMPW such that whenever the assembler sees the label, it substitutes the equated value at build time. Jeff Johnson http://home.dialix.com/~u2263/index.htm __________________________________________________ Do You Yahoo!? Get email at your own domain with Yahoo! Mail. http://personal.mail.yahoo.com/ -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

They are assigning the variables TEMPW and TEMPS to specific RAM addresses (that they apparently know or assume are available for their specific usage). The variables REGA and REGB are being assigned to addresses relative to the first two variables. There are other (more elegant) ways to assign variables to memory locations, that are probably more convenient in terms of porting the code to another processor or performing code maintenance (look into the CBLOCK pseudo-op). My terminology on these items may not be the most appropriate as I am also new to the PIC thing. I hope I have helped you in some way. Have fun. Michael Brown Instant Net Solutions http://www.KillerPCs.net {Original Message removed}

wait a minute, all registers are 1 byte wide for all pics, true? ----- Original Message ----- From: "rad0" <rden25KILLspamMINDSPRING.COM> To: <.....PICLISTKILLspam.....MITVMA.MIT.EDU> Sent: 15 April, 2001 21:03 Subject: Re: [pic]: beginning assembly question {Quote hidden}> Thanks very much, > > I forgot to ask, is it assumed to 1 byte in memory, or is this > something for each processor? > > > for > 0x20 > and > 0x21 > > is 0x21 1 byyte away from 0x20 ? > > > ----- Original Message ----- > From: "Jeff Johnson" <EraseMEj3ffjspam_OUTTakeThisOuTYAHOO.COM> > To: <PICLISTspam_OUTMITVMA.MIT.EDU> > Sent: 15 April, 2001 20:40 > Subject: Re: [pic]: beginning assembly question > > > > > what are these equate statements doing? > > > > > > Is this assigning the var labels to positions in > > > memory or > > > setting aside memory space, or what? > > > > > > ; VARIABLE DECLARATION > > > > > > TEMPW EQU 0x20 > > > > Yes. This is assigning a label to an address in > > memory. This allows you to write your code as > > > > movf TEMPW,W ;load W with contents of > > address 20 > > > > instead of the more cumbersome > > > > movf 0x20,W > > > > or assigning a value to a label > > > > movlw TEMPW ;load W register with value > > assigned to TEMPW > > > > such that whenever the assembler sees the label, it > > substitutes the equated value at build time. > > > > Jeff Johnson > > http://home.dialix.com/~u2263/index.htm > > > > __________________________________________________ > > Do You Yahoo!? > > Get email at your own domain with Yahoo! Mail. > > http://personal.mail.yahoo.com/ > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body > > > > > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Strictly speaking, each EQU assigns a value to its associated label. For example, TEMPW is not a memory location, but an assembler constant defined as having the value 0x20. It just so happens that it also represents a physcial memory address. To specify a label as being a physcial memory address (instead of simply a constant) use RES. Douglas Wood Software Engineer TakeThisOuTdbwoodEraseMEspam_OUTkc.rr.com Home of the EPICIS Development System for the PIC and SX http://epicis.piclist.com > {Original Message removed}

Strictly speaking all you are doing is assigning the label "TEMPW" to the number 0x020 (32) (and so on). What you use them for (memory address, location in register space, number of coffee beans in a decagram or whatever) is totally up to you. The assembler couldn't care less as long as it is within the range required for the destination. This is a *really* subtle point and one that is important to remember because I continually see new PICmicro programmers get messed up on it. The reason why it is confusing is that most new programmers assume the assembler is a lot smarter than what it is. I'm being pedantic because of your follow up question ("I forgot to ask, is it assumed to 1 byte in memory, or is this something for each processor?"). The only thing assumed is that each label is assigned to a constant. The four labels below could be declared using: CBLOCK 0x020 TEMPW TEMPS REGA REGB ENDC or ORG 0x020 TEMPW ORG 0x021 TEMPS ORG 0x022 REGA ORG 0x023 REGB or using the equate symbols that you have specified below. In any of the cases, you can use the labels as constants, register addresses or program memory addresses. To keep the usage of the labels for different purpose separate, I use the four conventions: 1. For variable registers, I use the CBLOCK directive. Note that with the CBLOCK statement, you have the option of specifying how many the counter is incremented by (the default is one) before the next label's value is assigned. 2. For program memory address, I define the labels in the source code as I show above. 3. For numeric constants, I use the "EQU" directive as you have done. 4. For variables within conditionally assembled code, I use the "define" directive. This allows a great deal of flexibility in programming, but it is often not for the faint of heart. myke {Original Message removed}