On 12/02/2017 05:12 AM, Frederic RIBLE wrote:
On 2017-12-02 11:24, Gene Heskett wrote:
I'd have really serious doubts anybody ever considered
the transmission
line termination characteristics needed to preserve a
perfect square
wave anyway. And if I asked that of the guy at Lowes
spooling off 100
feet of that cable for me, he'd think I was suddenly
talking in swahili.
Many MODBUS/RS485 papers are talking about 120 ohms bus
termination and signal reflection effects.
http://www.ti.com/lit/an/slla272c/slla272c.pdf
Most twisted pair cables, over a wide range of wire sizes,
come out to somewhere around 110 Ohm differential
impedance. So, anything between 100 and 120 Ohms works out
pretty well for termination.
Jon
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