Ethernet vs Serial Communication

Simplifying, what makes the big difference is that Ethernet uses biger and addressable data chunks plus continous negotiation so data verifying and resending if needed is done easier (regardless the distance that gives varied signal latencies) if that's what you ask. S.M.

Posts #3 and #4 have got down to the physical differences between Ethernet and the other serial standards [Ethernet is definitely serial].

RS232 used positive and negative potentials on the transmit wire, relative to a common wire. Transmit levels were 7 to 30 volts, while the minimum receive level was 3 volts. Transmitters were short circuit proof basically by having a lot of series resistance (2kohm comes to mind). Because of the high source resistance, much higher than cable natural impedance, cable capacitance attenuated the signal and slowed the + to - transitions so much that even 9600 baud could be a problem over 10 metre run. The standard was meant for just one transmitter and one receiver on a run - no provision for isolating transmitter or multiple receiver loadings. It was designed for connecting to a telephone modem, with multiple hardware handshake wires as well as transmit and receive. For other purposes, it was total pain - unless all the handshakes were provided or fooled - even a simple direct connection would not work. To add to the trouble, connecting a wire to the same connector pin number at both ends was OK for computer to modem, but you had to have "cross-over" connection for computer to computer. Also, the standard did not define connectors, not even to the extent that modems had female or male connectors!

RS422 recognized that cable pairs carry AC signals with minimum attenuation and reflections (echos cause data errors) if driven and loaded at their characteristic impedance and required a 100 ohm line impedance. Transmitters were differential, essentially connecting one wire to +5V and the other to 0 V for "space" (logic 1) [practicalities of drivers on 5 volt supply meant actual minimum differential transmit level was 2V] and swapping the polarities for "mark" (logic 0). A receiver sensitivity of +/- 200 mV and the differential signal allowed 10 Mbits/sec over short distances and 100 kbits/sec over 1200 metres. Up to 10 receivers could be connected to one transmitter/line.

RS485 extended RS422 with "open circuit" mode for transmitters, allowing up to 30 transmitter/receiver points on one line.

Ethernet also drives lines at their proper impedance (originally 50 ohm coax) but had another physical difference in that AC transformer coupling/isolation was practical because of Manchester coding (the signal polarity is always swapped at the end of each bit and a swap in the middle of the bit differentiates between mark and space). Also the high basic bit rate of 10 Mbit/s meant the transformer size was small.

In contrast, the RS serial link standards [100 bit/s up] assumed a DC wired connection without isolation, so a string of 64 zeroes is no problem. RS are hardware standards, word lengths of 64 bits plus start/stop or more are not excluded!

Hi friends....

Thank you very much for all these information.....

All re really helpful...

Skasnl