RS485 Driver

RS485 sounds like just another serial protocol

RS485 sounds like just another serial protocol which no one really uses anymore. Sadly, this cannot be further from the truth – read on to find out about its benefits and about an IC which makes implementing it really easy.

Differential signaling is helpful wherever noise can interfere with your signal: Jacob’s classic on Industrial Control Electronics can read as a collection of horrors of sorts. RS485 finds a home not only in the cabin of many aircraft, but – for example – also in some advanced model railroad systems.

Sadly, designing and RS485 transceiver by hand – while possible – definitely is not comfortable experience, especially for process computer jockeys who have a healthy respect of all things related to analog circuit design.

Fortunately, Analog Devices comes to the rescue with their ADM483E. Their IC contains both a sender and a receiver component, as can be seen by looking at one of the examples given in the datasheet:

A decoupling capacitor is all which is needed for your new RS485 bus.

The part generates all voltages on the fly – as long as the supplied 5V is relatively stable, the rest is handled automatically.

Need for speed!

Another interesting aspect is its high-speed – while many “ready” transceiver modules lack speed, the parts can work reliably at up to 250kbps. Of course, the part also supports multidrop, allowing you to add up to 32 nodes to your RS485 network.

Should you find yourself working on an environment where certification is required, Analog also has you covered. Not only is the company – it recently brought Linear Technology – of excellent repute; the part itself is intended to work with TIA and EIA standards. Pricing, of course, is quite humane – see pricing.

For the capacitor, in principle, any part can be used. As it must smooth out switching transitions, the use of a high quality decoupling part is recommended. These parts are not particularly expensive, and a single failed certification test can pay for literally thousands of them.

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