Post by thread:Novice Code and Data Addressing ?

Greetings, I am working on a micro controller project using the PIC16C84 chip. I am confused about one point and am hoping someone can offer a bit of clarification.... How do you differentiate between the location of a variable (temporary read/write storage) program memory (executable code) ??? Back in the days when we were using separate CPU, RAM and EPROM chips it was easy to figure out what was where in the memory map. After reading through the PIC16C84 documentation, I am not sure where the registers, general purpose registers and program memory start and stop. Is there a white paper somewhere on the Internet that might make this more clear ??? If this question is discussed in a FAQ somewhere, I would appreciate a pointer... Bob Segrest

Thus spake Bob Segrest (spam_OUTbobslanTakeThisOuTEROLS.COM): > How do you differentiate between the location of a variable (temporary > read/write storage) program memory (executable code) ??? RAM and ROM are in separate address spaces - on the 12 and 14 bit PICs there is no way to read code address space. In the memory map the address for code and data overlap - they both start from zero. the 16 bit PICs (17Cxx) have instructions to read from program memory, but you can only do so with these special instructions. This is a typical Harvard architecture, same as the 8051, as opposed to a Von Neumann architecture, where code and data are in the same address space, like a Z80 or 68xx. -- Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3354 2411 .....clydeKILLspam@spam@htsoft.com | P.O. Box 103, Alderley, | Fax: +61 7 3354 2422 http://www.htsoft.com | QLD, 4051, AUSTRALIA. | --------------------------------------------------------------------------- Download a FREE beta version of our new ANSI C compiler for the PIC microcontroller! Point your WWW browser at http://www.htsoft.com/

Thanks for the quick response... ;^) OK, this makes sense.... When I use the MPASM assembler, how do I declare/allocate RAM storage ??? If I want to use three single byte variables, is this the right way to do it ? ORG 0000 Temp1 DB ; first storage location Temp2 DB ; second storage location Temp3 DB ; third storage location Bob Segrest At 01:58 PM 2/9/97 +1000, you wrote: {Quote hidden}>Thus spake Bob Segrest (bobslanKILLspamEROLS.COM): > >> How do you differentiate between the location of a variable (temporary >> read/write storage) program memory (executable code) ??? > >RAM and ROM are in separate address spaces - on the 12 and 14 bit PICs >there is no way to read code address space. In the memory map the >address for code and data overlap - they both start from zero. the >16 bit PICs (17Cxx) have instructions to read from program memory, >but you can only do so with these special instructions. This is a >typical Harvard architecture, same as the 8051, as opposed to a Von >Neumann architecture, where code and data are in the same address space, >like a Z80 or 68xx. > >-- >Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3354 2411 >.....clydeKILLspam.....htsoft.com | P.O. Box 103, Alderley, | Fax: +61 7 3354 2422 >http://www.htsoft.com | QLD, 4051, AUSTRALIA. | >--------------------------------------------------------------------------- >Download a FREE beta version of our new ANSI C compiler for the PIC >microcontroller! Point your WWW browser at http://www.htsoft.com/ > >

Thus spake Bob Segrest (EraseMEbobslanspam_OUTTakeThisOuTEROLS.COM): > When I use the MPASM assembler, how do I declare/allocate RAM storage ??? I'm not the best person to ask about this, since I don't use the MPASM assembler. But I have seen other people do this: ScratchPadRam equ 0x20 AA equ ScratchPadRam+0 BB equ ScratchPadRam+1 CC equ ScratchPadRam+2 Note that the addressable RAM does NOT start from 0 - the registers like the timer, indirect register etc. are located in low memory. Check the memory map in the data sheet (it's on the web at http://www.microchip.com if you don't have it). Clyde -- Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3354 2411 clydespam_OUThtsoft.com | P.O. Box 103, Alderley, | Fax: +61 7 3354 2422 http://www.htsoft.com | QLD, 4051, AUSTRALIA. | --------------------------------------------------------------------------- Download a FREE beta version of our new ANSI C compiler for the PIC microcontroller! Point your WWW browser at http://www.htsoft.com/

Thanks Clyde, I think you have given me what I need... Bob Segrest At 02:36 PM 2/9/97 +1000, you wrote: {Quote hidden}>Thus spake Bob Segrest (@spam@bobslanKILLspamEROLS.COM): > >> When I use the MPASM assembler, how do I declare/allocate RAM storage ??? > >I'm not the best person to ask about this, since I don't use the >MPASM assembler. But I have seen other people do this: > >ScratchPadRam equ 0x20 >AA equ ScratchPadRam+0 >BB equ ScratchPadRam+1 >CC equ ScratchPadRam+2 > >Note that the addressable RAM does NOT start from 0 - the registers like >the timer, indirect register etc. are located in low memory. Check the memory >map in the data sheet (it's on the web at http://www.microchip.com if you don't >have it). > >Clyde > >-- >Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3354 2411 >KILLspamclydeKILLspamhtsoft.com | P.O. Box 103, Alderley, | Fax: +61 7 3354 2422 >http://www.htsoft.com | QLD, 4051, AUSTRALIA. | >--------------------------------------------------------------------------- >Download a FREE beta version of our new ANSI C compiler for the PIC >microcontroller! Point your WWW browser at http://www.htsoft.com/ > >

Bob Segrest wrote: {Quote hidden}> > Thanks Clyde, > > I think you have given me what I need... > > Bob Segrest > > At 02:36 PM 2/9/97 +1000, you wrote: > >Thus spake Bob Segrest (RemoveMEbobslanTakeThisOuTEROLS.COM): > > > >> When I use the MPASM assembler, how do I declare/allocate RAM storage ??? > > > >I'm not the best person to ask about this, since I don't use the > >MPASM assembler. But I have seen other people do this: > > > >ScratchPadRam equ 0x20 > >AA equ ScratchPadRam+0 > >BB equ ScratchPadRam+1 > >CC equ ScratchPadRam+2 > > > >Note that the addressable RAM does NOT start from 0 - the registers like > >the timer, indirect register etc. are located in low memory. Check the memory > >map in the data sheet (it's on the web at http://www.microchip.com if you don't > >have it). > > > >Clyde > > > >-- > >Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3354 2411 > >spamBeGoneclydespamBeGonehtsoft.com | P.O. Box 103, Alderley, | Fax: +61 7 3354 2422 > >http://www.htsoft.com | QLD, 4051, AUSTRALIA. | > >--------------------------------------------------------------------------- > >Download a FREE beta version of our new ANSI C compiler for the PIC > >microcontroller! Point your WWW browser at http://www.htsoft.com/ > > > > The general purpose registers start at 0x0C on the 16c84.Download the data sheets from the microsheet web site for remaining Special function register addresses There are 36 consecutive words of gpr.Tony M.