Greg Hartung wrote:

>   What would be an appropriate crystal for a 20mhz chip for the real-
> seconds discussion that's been going on?

  Try 20 MHz.  I'm puzzled.  I *think* I posted a message detailing a
real easy, concisely coded and dead-accurate approach to using even-
Megahertz crystal frequencies, but no-one has acknowledged it.  Did it
not get through or what?

>  I don't know how to get a multiplier of 5 in base 2.

  Do you mean a divisor?  A divisor is a loop which decrements a counter
each pass and when it becomes zero (the PIC has a special instruction
for this, DECFSZ as does IIRC, the Z-80), reloads the divisor value
*and* performs the "every-so-often" action.  A number is a number in
whatever base, but powers of two can be manipulated more readily as
individual bits in a binary word.

>  Do I have to slow down to something like 16.384Mhz?

  No, see above, and previous messages (in archive?).

>  I have never done digital before... so what the heck are the caps for
> in the resonator circuit?

  They're part of the tuned circuit.  See the ARRL handbook, or "The Art
of Electronics" etc...  Use the values specified by the crystal
manufacturer.  No manufacturer?  Try 15 pF.  Doesn't work?  Get a
crystal that has a manufacturer.  There's only so much you can do with
junk!

>   The chip has a UART, so are the MAX232's of the world simply a
> CMOS<->RS232 voltage transformer?

  100% correct.

>   Is serial the only sane way talk to an LCD?

  No.  In fact it's only for wimps.  If you're a wimp in this respect,
by all means go get a "Backpack" or similar assembly to play with, no
harm in that.  When you're through playing games, read the FAQs and
interface over a 4-bit bus.  You then save the cost of the EXTRA PIC or
whatever to do the serial-to-parallel interface.

  To *learn* the interface, I highly recommend using the parallel port
(using an extra card, not the one built into your motherboard) on a PC
with FORTH as the access language.  That mastered, do it in PIC.

>  Are the A/D's reversable to D/A?

  No.  D to A plus comparator = A to D, but not the other way about.

>  If not, how do I output to analog stuff, such as a transister, which
> woulda been my "digitally controlled" power supply answer?

  To perform D to A, either
 1} buy a chip to do it
 2} Make a R-2R network and use 8 port bits, or a shift register and
fewer bits or
 3} Learn to do Pulse Width Modulation in software on a PIC output
(don't know whether 16F877 has such hardware).

  How analog is one transistor BTW?

>    And most importantly, I need more FLASH RAM, like 256K.

  Look at Atmel or Philips devices.  Out of my present field.

>    How does the PIC deal with -5V for stuff like Manchester?

  Manchester and -5V are mutually un-correlated concepts.  Care to re-
phrase?

>   OT: Can anybody explain why the Measurement specialities 3-axis gyro
> has X and Y at 45:?  This seems infuriating...

  WOT and, No.
--
  Cheers,
        Paul B.