Why is Ethernet Faster than RS485?

[ali50]

Hi all,

I cannot understand why ethernet would be faster than RS485. I read somewhere that RS485 is faster than RS232 because the output voltage range is smaller and so the transition between 0 and 1 is faster. Is it the same idea with RS485 and ethernet?

 

[kf6bbl]

RS232 and RS485 are both asyncronous serial. In other words, the receiving end has to figure out where the bits are in a serial stream. To do this, the transmitting UART will typically add a start bit and a stop bit, and is expected to be reasonably accurate on the baud rate. The receiving UART typically oversamples the input to 'find' the bits. Crude, but reliable up to a certain point.
That certain point comes when you are dealing with Megabit speeds. It becomes less practical for a UART to oversample an already fast signal.
The solution that Ethernet provides is an embedded clock. The receiving end extracts the clock signal, and then knows precisely where the bits are.
There are other techiques used to go faster, and pack more data in increasing the throughput, but embedded clocks are the main reason Ethernet is faster the RS485.

-Bill
CE Designer Forum

http://www.cedesigner.com