Re: PIC or Freescale HC08 ??

On Mon, 27 Mar 2006 00:52:27 -0600, the renowned <r.laury@xxxxxxxxxxx>
wrote:

Hi Group:
I've got a project that I'm contemplating that needs:

To read a keypad with 20 switches.
Control 7 digits of 7 seven segment displays.
Generate pulses for a small stepper motor. (full step and micro step)
Possible control of a brushless servo motor with encoder feedback.
Monitor a few simple sensors.
A few hundred bytes of RAM is enough.
Program size with lookup tables ect, should be under 4-6K.
Flash would be nice.

I've never worked with the PIC and looking at their product line up there's
just too many to chose from.
I have worked with the Motorola stuff (HC05) but they are not making anymore
HC05 parts.

The HC08 is the flash-based replacement for the HC05 in Freescale's
lineup, though they have recently announced a stripped version
HC08/5/4 for really cost-sensitive consumer applications. I forget
what they call it, but it's probably not of interest to you anyway.
The 08s are nice parts.

My question is, What PIC would you use to do the above. Or maybe use several
PIC's to get the job done?
Or would you just go for one of the bigger HC08's?

The core micro is not so important except how it might fit with your
experience and tools. If you're used to the 05, you'll probably find
the PIC rather irritating, especially the lower-end ones. Unless
you're very cost-constrained start with the 18f, 24f or d*** series.

Is the potential BLDC motor/tachometer input (quadrature input?)
concurrent with the stepper or 'instead of'?

You've got a number of fine-time resolution things going on at once
that can only tolerate a limited amount of jitter or delay in reading
them. That will determine the hardware you need. I see no reason to go
to multiple processors or expensive controller chips, it can all be
done with a single processor. Sounds like you need 4 or 5
timer-counter capture compare modules, which should simplify your
search. If you need quadrature input, that will further limit things
or you might choose to use some external logic there.



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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