Post by thread:PIC ICD. Beware aliased memory

James Paul wrote: > > All, > > What Mike says makes sense, but I cannot argue one way or the other > because I haven't tried it. I've only used the F877 to emulate > other processors. I try to get the memory placement as close as > possible to the chip I'm trying to emulate. And when I do emulate > a lower processor, I limit my memory usage to the amount on the > processor I'm emulating. This only makes sense and is basically > what I stated in my original post. And that is to use only the > peripheral modules that the processor you are trying to emulate on > the 877. And this includes memory. I thought that went without > saying. I guess not. So if you are emulating a lower part that Except that you forgot that the 16C87x parts alias the top part of memory into the lower page (F0-FF,170-17F,1F0-1FF =>70-7F) while the 16Cxx parts do not. If your 16Cxx code uses F0-FF, you're in for a nasty surprise when you try to emulate it on 16C87x parts. If you take advantage of this aliasing (great way to save bank switching in ISRs) , then your code breaks when finally written to the 'lower' devices. > has, say, 1K of memory, then on the 877, don't use more than 1K of > memory. > Granted, my method does not give a 100% emulation of the other parts, > but it is close enough that I can usually develop my code and get it > to work in the target processor with very little further debugging. Yes, as long as you remember the aliasing. You can't use that top 16 bytes of RAM for anything if you want transparent cross device compatibility. {Quote hidden}> I usually do what works for me, and saves me trouble. Using only > the 877 seems to have saved me trouble so far in that I have only > one processor to concern myself with, and as such, I have become > rather profecient with my method. This is not to say that there > aren't other, and possibly better, ways of doing this. But I'm > comfortable doing it the way I'm doing it, so I'll go that way. > > Regards, > > Jim > > On Thu, 25 May 2000, Mike Harrison wrote: > > > > > On Thu, 25 May 2000 06:24:42 -0700, you wrote: > > > > > Andrej, > > > > > > The ICD comes with a 16F877, but you can emulate almost any lower > > > part by using only those peripheral modules included with the lower > > > part. I've used the ICD to develop code for the 877, the F84, and > > > even the C672 and other 8 pin parts. > > But this is not always the case - if you're using RAM locations in > > upper banks, e.g. on the 874 - it is significantly different on the > > 877. > > An '874, however is a suitable development platform for many of the > > other 16cxx devices, so it's useful to have an '874 and and '877 to > > hand. > > spam_OUTjimTakeThisOuTjpes.com