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[DPRG] Microcontroller network questions

Subject: [DPRG] Microcontroller network questions
From: Randy M. Dumse rmd at newmicros.com
Date: Wed Aug 10 14:29:51 CDT 2005

> What I'm wondering is, does such a thing currently
> exist?

We've got a couple products very close to what you describe.
We've got our TiniPod(TM), PlugaPod(TM) which have 24/48 pins
with built in CAN. They can bit bang 12C, but that's not as
satisfying as just running a CAN bus. And they have SPI for
local interconnections.

We've also got (in similar format) a TiniARM(TM) with I2C on it,
and a PluganArm(TM) (renamed Pluga2129(TM)) with both I2C and
CAN on board. Each has regulator, RS-232 buffering, debug LED's,

(And we've got similar format AVR's, but they lack CAN.)

> How do you guys feel about RS485 and a custom
> protocol vs CAN?

I wanted to see if anybody else would say anything about CAN. I
didn't see much on CAN in your replies.

I used to fear CAN. It sounds so complicated with all the
acceptance filters, etc. Don't make it too hard. Once you set up
the registers (I run them wide open and look at every message
that comes through because it is so easy to do) it is as close
to a set and forget communications as you can get.

Basically, when a message for you shows up (with all messages
not for you filtered out if you like) it's laying in the buffer.
Take it and you're ready for the next one to come in.

Also you set up a reply message in a buffer, and toggle a bit,
the whole message is gone, and you get an acknowlege when the
other unit reads it. Basically, if it doesn't get through
(collision or noise or what have you), it keeps trying until it
gets it through, or times out. Imagine, retries without any
software intervention!

You just can compare anything else to the ease of CAN, once its
going. And you have got to remember, this thing is THE choice
for automotive applications so you know its nasty environment
compatible. You just about can't do better than CAN. My opinion,
forget the 485, and the protocol, and the software over head,
and the noise, and the lost messages, and the collisions, and
the worries about through put (500KHz). Switch to CAN and breath
easier. In fact, if the Atmel is the reason you're not doing
CAN, dump the Atmel in favor of a processor with CAN. It's that
good (imho).


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