[Q]: external RAM for PIC

Strange, sure, but that's what this chip was designed to be like. Actually, if memory serves me well, you should consider yourself rather lucky you even got as many as 3840 bytes of RAM --- other PICs have even less.

It almost certainly doesn't make sense.

I strongly doubt any RTOS not written explicitly for the PIC can ever be ported to it. That platform is just too weird for such an effort to work out. In other words: if you want another platform to port your existing RTOS to, PIC is almost certainly not it.

Forget it, PIC is not a good choice.. it's ok for mickey mouse stuff, but for serious applications, choose something more appropriate..

You are making the mistake of equating "small" with "not serious". There are plenty of small serious applications for which the PIC is perfectly appropriate, although most of them would have no use for the OP's RTOS.

-Robert Scott Ypsilanti, Michigan (Reply through newsgroups, not by direct e-mail, as automatic reply address is fake.)

You'd be wrong, then. I've been involved in developing three RTOSes on PIC18 hardware, all of which we had ported from more conventional non-Harvard machines. Much of what we discovered on the PIC helped us to port to DSP architectures too.

pete

Becuase the PIC has a Harvard architecture where the code and data spaces are completely separate as opposed to a Von Neuman architecture where the code and data share the same space like in most Motorola micros.

IAn

Means the data space can not be expanded ?

Three ?! Then I should concentrate on another CPU ;-)

These are strange too. Right.

So maybe I should start and take it as exercise :-)

The data space on some PICs can be expanded with external memory, but you lose a lot of your ports. Just look for "External Memory" in the datasheets.

Peter

micros.

I did. And from my understanding you can access data only thru the table-opcodes.

What I hoped is an expansion to the real data space, i.e. data RAM I can read directly without the need to use special opcodes.

But I see, it is not (yet ?!) possible to expand the register map.

Additional data can be read or writtened to EEPROMs, serial flash, or FRAM chips throught the SPI interface. If you are looking to directly address the memory, it probably would be best to consider a different architecture than PIC. The PIC was designed for small embedded control projects and does this job well. However, it has never been the best choice for handling large tables or data blocks. You might take a look at the NEC K0 series if you are looking for an 8 bit that handles external memory well.