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'The Ultimate Peripheral: Another PIC'
1998\07\25@123854 by Thomas McGahee

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For the sake of newcomers to the PIC, I offer a few ideas.

Sometimes I notice people trying to use a single PIC to do
everything, and eventually ending up with lots of extra
peripheral chips such as shift registers hanging off of
the PIC to implement the extended I/O. I do this myself,
when the I/O load is low and the programming load on the
PIC is reasonable.

But sometimes I find it easier to simply use one or two
serial lines and communicate my extended I/O needs to
another PIC.

I often 'steal' my clock from the master PIC. That also
guarantees that both PICs are running the same speed.

An example that most of us are familiar with is the PIC
used as a controller for an LCD module. It communicates
in series using standard UART protocol.

One of my PIC controllers is a
multi-digit LED driver with enough intelligence
to directly convert binary numbers into BCD and then
decode for direct 7 segment readout.

I have one of these that accepts 8 bit data and then
determines whether a number was sent, or a command, or
a request for one of many messages. Yep, you can
display a fair amount of text on even dumb 7 segment
readouts.

You can really blow people's minds when you have the cute little 7 segment
displays do things they didn't know could be done. When I have extra
code space left over in a PIC I sometimes use it to perform these visual
tricks right after power up. You can form reasonable facsimiles of the
following: a b c d (e) f (g) h i l n o r t u  A B C D E F (G) H I J L (N)
O P S (T) U Y (Z) 0 1 2 3 4 5 6 7 8 9. So you can send out messages such
as <Hello Bill> by scrolling the data to the left slowly.

You can do some simple "animations" by having the segments appear to
walk around in circles. You can do very small circles (1/2 digit),
regular 1 digit circles, larger 2 digit circles, etc.  You can afford
to do this sort of craziness when you have a PIC dedicated to
performing the i/o.

I prefer to build Intelligent sensors.

When building your own PIC intelligent controllers, you
can opt for a two wire communications interface that can
run rings around the regular UART method. First of all, you
can define a packet protocol that allows you to dump
lots of info in one packet without the start/stop overhead
for every byte. Secondly, one of the wires carries sync
clock info so you are not dependent on the crystal
frequency. Set up a Bit and change the sync line. The receiving
PIC 'sees' the sync line change and inputs the Bit data.
Once a packet is fully received, then the receiving PIC processes
it and uses it, while the sending PIC goes on its merry way
with other tasks.

Fer what it's worth...
Fr. Tom McGahee

1998\07\26@043549 by paulb

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Thomas McGahee wrote:

> You can form reasonable facsimiles of the following: a b c d (e) f (g)
> h i l n o r t u  A B C D E F (G) H I J L (N) O P S (T) U Y (Z) 0 1 2 3
> 4 5 6 7 8 9. So you can send out messages such as <Hello Bill> by
> scrolling the data to the left slowly.

 I can accept that l = I = 1, Z = 2, S = 5, B = 8, g = 9, O = 0, but I
can't really see how you can distinguish D from O or f from F.

> You can do some simple "animations" by having the segments appear to
> walk around in circles.

 Yes, real neat!

 Can you explain your two-wire protocol a bit more?
--
 Cheers,
       Paul B.

1998\07\26@080623 by wwl

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On Sat, 25 Jul 1998 12:34:34 -0400, you wrote:

>For the sake of newcomers to the PIC, I offer a few ideas.
>
>Sometimes I notice people trying to use a single PIC to do
>everything, and eventually ending up with lots of extra
>peripheral chips such as shift registers hanging off of
>the PIC to implement the extended I/O. I do this myself,
>when the I/O load is low and the programming load on the
>PIC is reasonable.
>
>But sometimes I find it easier to simply use one or two
>serial lines and communicate my extended I/O needs to
>another PIC.
>
>I often 'steal' my clock from the master PIC. That also
>guarantees that both PICs are running the same speed.
The 12Cxx series are especially good for this - no need for any clock
distribution, cheap and small. The A/D versions (67X) can be used as a
complete 'smart' analog acquisition subsystem - sensor power control,
calibration, input change detection etc. etc.
    ____                                                           ____
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_/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

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