Post by thread:[PIC]: 18f MPASM warning

I am making my first steps into 18Fxxx programming. When asembling something like goto 1 I get the warning 'Destination address must be word aligned'. I see bo hints in the 18F datasheet of such a restriction. The warning seems to happen only when the destination is specified as a value, not when it is a label. What is going on? Wouter van Ooijen -- Van Ooijen Technische Informatica: http://www.voti.nl Jal compiler, Wisp programmer, WLoader bootloader, PICs kopen -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

>I am making my first steps into 18Fxxx programming. >When asembling something like > goto 1 >I get the warning 'Destination address must be word aligned'. >I see bo hints in the 18F datasheet of such a restriction. >The warning seems to happen only when the destination is >specified as a value, not when it is a label. What is going on? Exactly what it says. You will find a word aligned value is always an even value, and a label will implicitly have this because of the way it is assigned. You should not have a problem with "goto 2" or "goto 0" -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

Hi Wouter Check figure 4-5 of the 18F452 data sheet. You can address each word as individual bytes in case you want to store data in the program memory but the instructions words are aligned on even byte boundaries. Dave > I am making my first steps into 18Fxxx programming. > When asembling something like > goto 1 > I get the warning 'Destination address must be word aligned'. I see bo hints > in the 18F datasheet of such a restriction. The warning seems to happen only > when the destination is specified as a value, not when it is a label. What > is going on? > > Wouter van Ooijen -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Wouter van Ooijen wrote: >I am making my first steps into 18Fxxx programming. >When asembling something like > goto 1 >I get the warning 'Destination address must be word aligned'. I see bo hints >in the 18F datasheet of such a restriction. The warning seems to happen only >when the destination is specified as a value, not when it is a label. What >is going on? If you have been using other PIC families, there are some things that you need to understand about the PIC18 family. First off, it's program memory is BYTE oriented rather than WORD oriented. This means that every 16-bit instruction takes two bytes of program memory (double word instructions take four bytes), so the instructions are ALWAYS aligned on even addresses. So GOTO 1, or GOTO <any odd address> is not a legal instruction. You cannot jump into the middle of an instruction and the PC will always be even aligned. This architecture helps the compiler quite a bit when dealing with transferring data from program memory to file registers, and the latest MPLAB C18 C compiler v2.00 is very efficient. In fact if you actually look at the hex values for the instructions, there is no way to "encode" the odd addresses. Addresses are actually "shifted right" by one when encoded. The nice thing about the 18Fxxx is that there are no program memory "pages" and data memory can be accessed as a linear 4K array using the FSR registers. Register banking is still required to do direct access to most file registers, but SFRs can be addressed without banking. No more BANKSELs needed when changing a port from an input to an output. Darrel Johansen -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

> When asembling something like > goto 1 > I get the warning 'Destination address must be word aligned'. I see bo hints > in the 18F datasheet of such a restriction. The warning seems to happen only > when the destination is specified as a value, not when it is a label. What > is going on? On the 18 family, program memory is addressed in 8-bit bytes, but instruction opcodes are 16 bit. Each instruction must start on an even address, and the assembler can tell that 1 is not even. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

> Check figure 4-5 of the 18F452 data sheet. You can address each word as > individual bytes in case you want to store data in the program memory but > the instructions words are aligned on even byte boundaries. Thanks for the answers. When someone asks me why they should use PIC instead of AVR, 8051 etc. there is always one unexpected argument from my side: http://www.piclist.com (both for the list itself and for the PIC techref pages). Wouter van Ooijen -- Van Ooijen Technische Informatica: http://www.voti.nl Jal compiler, Wisp programmer, WLoader bootloader, PICs kopen -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

PIC18 instructions are 16 bits long while address refer to 8 bit locations. So, all instructions start on even addresses. Have a look at the absolute listing of your program. Harold On Wed, 19 Jun 2002 04:53:50 +0200 wouter van ooijen & floortje hanneman <@spam@wfKILLspamXS4ALL.NL> writes: {Quote hidden}> I am making my first steps into 18Fxxx programming. > When asembling something like > goto 1 > I get the warning 'Destination address must be word aligned'. I see > bo hints > in the 18F datasheet of such a restriction. The warning seems to > happen only > when the destination is specified as a value, not when it is a > label. What > is going on? > > Wouter van Ooijen > -- > Van Ooijen Technische Informatica: http://www.voti.nl > Jal compiler, Wisp programmer, WLoader bootloader, PICs kopen > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com Reach broadcasters, engineers, manufacturers, compliance labs, and attorneys. Advertise at http://www.hallikainen.com/FccRules/ . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body