Subject:
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Picking a PIC
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 27 Oct 1998 04:21:05 GMT
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Original-From:
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Clem Taylor <ctaylor@%Spamcake%srtc.com>
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Viewed:
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1447 times
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I'm looking to offload the processing of IR proximity sensors and
ultrasound to a PIC(s). I'm hoping to connect the PIC to a HandyBoard via
the SPI.
I'm trying to decide which is the right PIC for the job.
The PIC16C7x (PIC16C76) series supports SPI, can source 25mA/pin, 2 PWM
channels, and has 22 I/Os with 5 ADCs. Cool part! However, many people
seem to use the PIC16F84 because it's based on flash, so you don't have to
wait forever to erase them, but it doesn't have all the cool features of
the PIC16C7x, specifically SPI.
Emulating SPI in software seems like a silly waste of cycles. I'd really
like to overlap taking measurements with sending data, which looks like it
could be difficult, if it's manually clocking bits out on the serial
interface.
What would you guys recommend as a good general purpose PIC? Digikey has
the PIC16C76/JW for $16.55 and the PIC16F84-04/P is $6.25. I'm planning
to use the PICProto18 or PICProto3 from microEngineering Labs. With PICs
being fairly cheap, it might be easier to just use multiple PICs rather
than handling the software complexity of doing everything in one chip.
Has anyone connected multiple PICs to a SPI bus, with the HC11 in master
mode and the PICs in slave mode? The 68HC11 docs I have are a little
sparse on how multiple slave mode works. Would I have one slave select
line to each PIC and then the HC11 code would have to poll the PICs by
selecting each one in turn with some sort of simple packet protocol? It's
ashame that the 68HC11 doesn't support I2C, because it seems that they
solve this problem with that interface...
We've got a nice programmer at work, so I shouldn't have any trouble
programming either chip. Another complication is that I don't have a PC,
so I was hoping to do all my development using one of the free assemblers
on my Unix box.
Thanks,
Clem
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