After yesterdays post on the differences between RS232 and RS485, we have been asked a few times why RS485 is more noise immune. It is because RS485 uses a differential signalling method. Here’s how it works, and why it’s effective:
🔗 Differential Signalling in RS485:
RS485 uses two wires to carry a pair of signals that are exact opposites (one is the inverse of the other). The receiving device compares the difference between the two signals to interpret the data. Since external noise usually affects both wires equally (common-mode noise), the difference between the signals remains unchanged, effectively cancelling out the noise. This is the reason that twisted-pair cables are often used in RS485 – the twisting ensures that both wires are exposed to the same noise levels, enhancing noise rejection.
⛓️💥 Why RS232 is More Susceptible to Noise:
RS232 uses single-ended signalling, where data is sent over a single wire relative to a ground reference. Any noise affecting the signal line or the ground reference directly impacts the signal, making it harder to filter out.
Saying RS485 is the winner is a bit disingenuous. As mentioned in the previous post, each has its advantages: choose RS232 if you need a simple, low-cost solution for point-to-point communication over short distances and use for RS485 when building a robust, long-distance network involving multiple devices, especially in noisy industrial settings.
