AVR-Chat

On Tue, Oct 05, 2004 at 05:42:54PM +1000, John Samperi wrote:

> 0x01 - invalid parameter or command not possible. This would be
> the response if one commanded a node to run at 115200 baud,
> but the node could not actually run that fast.
> 
> How would the node respond if it cannot communicate with the
> master? :-)

Specifically for configuration purposes, a jumper, switch, etc, should
be provided on the device to enter "configuration mode".  In
configuration mode, the line settings are preset to a known value.
Then the device can be configured using the described configuration
commands.  Upon reset, the new settings take effect.  At that time,
all nodes need to switch to the new settings, or they won't be able to
talk on the bus.

I think that what you are thinking in the example given above is that
the one node is running at 115200 and asking the other node to change
it's baud rate to match.  That's not the case - assuming configuration
mode is in effect (see the description of "Communications
Configuration" a little further down in the document), the line
settings are pre-arranged to known values.  After reset, the newly
commanded settings are then assumed.

> I use a similar "home brewed protocol" for our equipment, but
> without the flags field. The maximum data lenght is 255 bytes but
> I'm considering a long packets mode (2 bytes len) because some of
> our electronic signs need up to 450 chars.

We kept the data size in ROBIN fairly small because it's intended for
small microcontrollers where there is usually limited memory, and it
might be impossible to buffer large packets.  In practice, I haven't
found the 64 byte packet size of ROBIN too constraining.

> By the way it is not very difficult to use 9 bit mode with your PC,
> there is a thread on the subject on Avrfreaks.net. I thought for a
> long time that it would be hard without knowing that this facility
> has been available with the PC UART for about 20 years, just using a
> different name.  I'm currently working on a Delphi interface to our
> products using the 9 bit data protocol and it works like a charm.

Do you have a link to the thread - I'd be interested in that.

Thanks!
-Brian
-- 
Brian Dean
BDMICRO - ATmega128 Based MAVRIC Controllers
http://www.bdmicro.com/