CAN without transceivers

Reinardt Behm <reinhardt.behm@t-online.de> wrote:
> Uwe Bonnes (bon@hertz.ikp.physik.tu-darmstadt.de) wrote at Wednesday 14
> September 2005 10:49 in comp.arch.embedded:

...
> > 
> > Connect TX of each CAN interface to /EN of a HC125, drive each HC125 input
> > low and connect both HC125 output together and to RX of both interfaces
> > and pull up to VCC.

> You can do it even simpler:
> Take a diode with the cathode at tx and the anode connected to rx at every
> node and a common pullup-R (about 1k) and tie all rx's together.

With a At90can128 with a supply of VCC=3.3V and VIL (max)= 0.2*VCC=0.66V and
a voltage drop of about 0.65 Volt for a 1N4148 at 4 mA you are playing an
insecure game...

Even at VCC=5V, margings are not much higher if temperature drops.

In short, if you are playing around, use the diodes and save some cents,
otherwise use a more reliable approach. 

-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
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