What is termination resistor in RS-485?
120 ohm network termination resistors placed at the ends of an RS-485 twisted-pair communications line help to eliminate data pulse signal reflections that can corrupt the data on the line. But on the whole the termination resistors will help network performance more often than they will hurt it.
Is RS 422 compatible with RS-485?
RS-422 components are not RS-485 compatible and therefore should not be used in multipoint applications. Conversely, RS-485 components are RS-422 compatible, which is why Intersil’s portfolio of differential transceivers are RS485/RS-422 compatible.
What is the difference between RS485 and RS-422?
RS485 can have multiple Commanding Devices and multiple Listening Devices. RS422 can have only one Commander and multiple Listeners. For example, you can connect one PC (the Commanding device) to 10 temperature controllers (listeners).
Where to place termination resistor on RS-485 cable?
Place a termination resistor matching the cable impedance at a convenient location, as close to the end of the RS-485 line as possible. It’s possible that a node attached to the RS-485 line may have terminating resistors built into it as a configurable setting, so check that when adding termination resistors to any line.
What should the impedance of a RS-485 be?
Resistive terminators typically have values from 120 to 130 Ω. Although twisted-pair cable impedances can be as low as 100 Ω, a 100 Ω terminating resistor is too low for RS-485 drivers, because two in parallel yield 50 Ω, and RS-485 drivers are not rated for loads below 54 Ω.
How many devices are allowed on a RS-485 network?
On RS-485 networks only one device is allowed to communicate at a time; otherwise data collisions may occur. In master/slave protocols this is less of a concern, because the master is usually initiating requests and then slaves respond at that time.
When to use bias and termination in RS-485?
Biasing and termination are used to make an RS-485 network more robust and communication more reliable in certain RS-485 network designs. If you’re having communication problems on your network, termination and biasing are usually the first place to start in improving RS-485 network communication.