RS-485/422 termination resistors

[sweethomela8]

If I'm doing a point to point full duplex transmission for RS485 or RS422,
what parallel resistor value should I use as a termination?

Second, does the resistor only go at the receiving end?
(In other words, no parallel termination at the transmitter?

Thanks.

 

[IanP]

what parallel resistor value should I use as a termination?

Termination and Bias Resistor Information
http://www.national-instruments.com/support/serial/resinfo.htm

Second, does the resistor only go at the receiving end?

see attached picture ..

IanP

 

[BurnOut_tesla]

Termination resistor is required at both extreme ends.. Its value is abou 100-120 ohm
U need not use it every time.
If your transmission length is very long then calculate ur one bit period depending on your baud rate.
If one bit period is less than transmission time to extreme end then only u need to use it, otherwisw ur communication will work fine without termination resistor.

 

[sweethomela8]

**broken link removed**

After doing some research...

Take a look at page 20.

A termination resistor which should usually match the characteristic impedance of the line zo=120 Ohms is used at the receiving end only in full duplex applications which are point to point

In half duplex point to point, the termination goes at both ends since there are receivers at both ends which share lines with the transmitter (half duplex).

Anyone disagree?