>
>         I'm trying to decide on a chip to use in a "laptop" (more of a
> TI-85 for coding only) i'm going to make, the PIC17FR4x's look fast
> enough, and can handle enough memory for what i'm trying to do.

Up to 128K. Or more with bank switching/paging...

>  Is there
> to be a EEPROM version of this chip in the future?

Don't know. Most times whenever someone asks about more EEPROM parts
The response from Microchip has been along the lines of "too slow, not
cost effective, no request from real (read thousands of units).

But honestly for the 17CXX series makes it unnecessary because it's the
only PIC parts that can execute code from external memory anyway. So what you
can do is develop a loader in the internal EPROM that'll read the program
say from a serial EEPROM and load it into the external RAM, then execute it.
For development purposes it's fairly simple to load the external ram
directly from the development system into the external RAM. Or a combination
of both (development system -> on-board EEPROM via 17C42 -> external RAM
on reboot.

In any case you'll only have to program the 17CXX part enough times to get
a working loader, at which point you can program the board via the loader
program. It gives you the added advantage of removing the EPROM erase/program
step from the development cycle.

> (How many times can I
> erase/reprogram the current EPROM version?)

Not sure. it's in the data sheet. But EPROMs a designed to be erased/programmed
on the order of over 10,000 times. You'll probably not exceed the limit.

>  What kind of external memory
> should I use with this, is it difficult to use external memory?

In reverse order: No and static cache RAM for the average PC. The reason for
the second is fivefold:

1) the 32Kx8 skinnyDIP package is space saving.
2) commodity pricing makes them cheap. Real cheap. In fact it's quite ease
   to strip 256K of it from a non working PC MB with cache RAM aboard.
3) Fast. 20ns access time means no worries about the PIC outrunning it.
4) Can upgrade memory in 64K sements up to say 128K. Then look at a
bank switch scheme with larger memories
5) Static. no worries about refresh.

As for attaching it it's fairly simple, you add two 74X373/573 type latches
to latch the 16 bit address and then the PIC read/write a 16 bit data value.
It's all in the data book.
>
> I'm planning on using the following:
> - 320x(200/240) LCD

Does this have built in character/graphics drivers? If not then you'll probably
need another PIC to act as the interface to it. One of my biggest problems.
I have a Toshiba display from Timeline that I haven't gotten to work even
with the built-in drivers. Japanese translated English isn't real conducive
to easy understanding.


> - 1 Parallel Port / (1/2) Serial Port(s)

Be aware that the 17CXX only has one hardware serial port. If you want more
you'll have to add chips. I like the signetics 2691. Does anyone know of a
8250/16550 type chip that comes in a 28 pin skinnydip or smaller?

Be sure you make the parallel port 8 bit bidirectional....

> - At least 1mb of Memory

Bank switching or paging since the 17C42 can't handle it naturally? I've
always been partial to using a fast static RAM to act as a paging ram. Then
for each task you can map up to 128K of available memory from whatever pool
is available.

If you want that much memory you may want to consider another RAM alternative:
Pseudostaic. It's a dynamic RAM with refresh circuitry built in. All you have
to do is strobe the OE* line every once in awhile and it stays refreshed.
Nice thing is that it comes in 512Kx8 packages (Yup a 1/2 meg). So two chips
will give you a meg. Now once again who are you going to access it?


> - Qwerty keypad or mini-keyboard

When you find a source let me know. I have a mini (not micro) XT keyboard
(maybe 8 in across) that I'll get around to using one day....

And you still haven't dealt with a fundamental PIC flaw: the inaccessible
stack. It's significant because interrupt based task switching is almost
impossible to do because you can't change the stack for each task. Does anyone
know a workaround this short of completely implementing your own stack
by changing each 'call' into a 'push return address on my stack' followed
by a 'goto'? And even then presuming an interrupted based context switcher
how can you get the return address for the interrupt just to save it? Also
what's the effect of not doing a RETIE but instead a simple GOTO to the
next task? I've actually put a few seconds into thinking about the problem
and there's no easy way to solve it.

Even if Microchip had mapped just the top of the hardware stack into memory then
there's a possibility of implementing a usable multitasking executive. Because
the call stack can be easily implement using gotos and user stacks, A TOS
mapping would create the ability to store the current return address and change
it.  I mean it's only 2 lousy bytes that I believe each PIC has in its address
space. A real bummer.

But as it stands I don't see how to do it. I do see from my own discussion that
cooperative multitasking is possible by avoiding calls, but it's puts you in the
position of being one errant infinite loop from system lock-up.

This is the one IMHO fatal flaw in the PIC17CXX design that makes it
unsuitable for general purpose computing designs.

So given my criticism let me throw out an oldie alternative: The Motorola
68020. Why you ask?:

1) Everything I've discussed here applies
2) It can access up to 16 Megs of memory with no bank switching. Paging is
still a good idea.
3) There are a lot of good cheap peripherals that will implement the stuff
you want. Like the 68881 dual serial port.
4) Absolutely no stack problems. I mean if Sun can run Unix on it then your
multitasking executive should be no problem...
5) It only needs one external EPROM/EEPROM to get going. But you can have
up to a 32 bit wide data path for excellent memory performance...
5) You can get a 20 Mhz part from BGMicro for $9.95. Yup. 10 bucks.

The biggest downsides are:

1) Power Hungry. Like in hungry hungry hippo hungry.
2) No nice built in stuff. Just the CPU. Of course adding memory is just about
as simple as the 17CXX.

Another possibility in the Motorola family is the 683XX series. I don't know
about pricing, but they have an extended 68020 core (called CPU-32), on board
peripherals (serial, parallel, DMA, timers) and come in low power/ low voltage
versions. I'm partial the 68340 and the 68332 is nice too.

Anyway it looks like a fun task. Something like this is on of the myriad
tasks on my design list: specifically a semi-portable, very flexible MIDI
sequencer. Of course that tast has been on my list longer than the completion
of my PhD (and I started that 6 years ago...)

Have Fun.

BAJ