'Multi-drop serial bus'
> There was a thread on the list a while back about implementing a
> multi-drop serial bus for PIC communications (RS422, I believe). Can
> anyone help me find it? I would like to know the resolution, ie, did
> they find a way to do it? Is there existing code to implement this bus?
> Any help appreciated.
> Martin Kirk
> Arizona State University
> (602) 263-9270
I don't remember the discussion but let me explain something that works
quite well for me at low data rates (1200 baud). I haven't hooked it to a
scope to see the waveforms but I THINK the design is sound. What I do is tie
the Rx line going to the computer to RTS through a 2.2K resistor. I write my
programs to pull RTS low (-12V). I then connect the Rx line through an
opto-isolated transistor to +12V. I can then switch the line from -12V to
+12V by energizing the optoisolator. Also, I can connect many of these
together this way. Then, I just connect the Tx pin of the computer to all
my PICs through a large resistor (I think I used 1Mohms so there was very
little loading). Now, you have to work on your protocol because collisions
can definately take place. Also, a limitation is that you cannot have one
PIC talk to another - just to the computer.
If anyone has any comments on this, I'd like to hear them. I've been
using this method for a long time - with no problems at all.
-- Paul Greenwood -- (austin.ibm.com) pablo
"We don't care. We don't have to. We're the Phone Company."
More... (looser matching)
- Last day of these posts
- In 1995
, 1996 only
- New search...