AVR-Chat

You can run SPI pretty slow.  Since each line (MISO, MOSI and SCK) are
uni-directional, you could buffer them, or even use LVDS (but then where
would the simplicity be...)  SPI is really simple, primitive and you can
hang simple shift registers off the end.  The disadvantage of SPI is that
you need some sort of "enable" line for each peripheral.

TWI is another possibility, again, it was designed for board level
interconnect so 20ft is a stretch.  But, again, you can run it pretty
slow... but the device addressing is built into each part.

The only other solution would be some sort of multi-drop serial interface.
Or, to add external hardware to your AVR chips.  I assumed from the start
that you wanted to use minimal external components to make this work.



-----Original Message-----
From: James Washer [mailto:washer@trlp.com]
Sent: Wednesday, November 24, 2004 7:32 AM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] Re: Any general length considerations for SPI
busses?



I'm a newbie at playing with HW.. I've been a software guy forever. Sorry
for leaving out details.

I've got a couple of different situations.

1) I want to have a remote AVR with an LCD that shows system status. Nothing
major, but with any of say 20 inputs( think automobile, door open, oil
pressure low, ignition on, etc). The LCD needs to be updated with things
change.  The AVR/LCD unit will be ~10 feet from the main controller.

2) Think home alarm/automation system. Temp sensors, door sensors, smoke
alarms, motion detectors, etc. These "sensors" will be up to ~100 feet away

In neither case do I need much speed. I don't have any hard number here, but
I'd thinking tens of bits/second is all I need.

p.s. What is LIN??

 - jim

On Wed, 24 Nov 2004 14:40:04 -0000
"Graham Davies" <YahooGroups@ecrostech.com> wrote:

>
> --- In AVR-Chat@yahoogroups.com, James Washer <washer@t...> wrote:
>
> > ... working on a system ...
> > ... a few "remote" devices
> > (ADC, Temp sensors, etc)...
>
> People would be able to help you more if you gave us some idea of the
> data rate you envision.  SPI can be pretty fast - do you need that?
> The suggestion to use CAN probably assumes you do. Cheaper and easier
> alternatives exist if a lower data rate would do.  An example would
> be LIN.  Anyway, as people say, SPI is not right for your application.
>
> Graham.
>
>
>
>
>
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