At 10:13 AM 9/24/96 GMT+1100, TONY NIXON 54964 wrote:
>The easiest way to connect multiple IO lines together is to use an
>open collector driver.
>

This isn't a good idea for long wire lengths. Open collector circuits have a
higher impedence output stage, that combined with line capacitance will
degrade the overall speed (effective bps). Your system might work great in
the lab but watch out when you put it in the field.

Not to mention switching noise, like motors etc., could induce voltage
spikes into the PIC which might damage it or most certainly affect the
communications.

Also, if you power the devices in a home or where ever, there's a chance
that the "ground" potential difference exceeds some PIC rating which might
also damage it.

How do I know this? I design industrial spread spectrum modems with a PIC
front end with either 232 and 485 interfaces.

Stick with 485.

craig

____________________________________________________
Dr. Craig Hollabaugh
Wireless Scientific, Inc.
1890 S. 14th, Suite 105
Amelia Island, FL 32034
904 261 6977
904 261 2129 fax
wsci@net-magic.net