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#Serial communication protocol comparison serial

This is known as full-duplex communication.

This has the advantage of enabling the master device to transmit to the slaves while a single slave device may also transmit back to the master simultaneously.

It's TX pair is connected to all the other "slave" devices' RX pairs, and all the slave's TX pairs are tied to the master's RX pair.

In 4-wire mode, a single RS485 device is designated as the "master" device.

An advantage to this topology is that you can save on cabling cost since the cable can be several thousand feet in length.

In 2-wire mode, only one RS485 device can transmit at a time, this is known as half-duplex communication.

#Serial communication protocol comparison serial

RS485 serial "networks" can be wired for 2 or 4 wire mode.No isolation transformer is needed as in Appletalk described below.This is achieved by having an "output enable" on the TX ports and allowing only one RS485 device to transmit at a time on a given pair of wires.There can be up to 32 RS485 devices on a single set of serial lines. It adds a slightly wider input voltage range on its RX pair, to make it less susceptible to noise and GND potential differences among RS485 devices. RS485 uses differential TX and RX as in RS422, however RS485 is a superset of RS422.These wire pairs also reduce the impact of external electrical noise on the signaling.If twisted pair cabling is used, (which makes sense because you end up with a complementary TX+ and TX- pair and RX+ and RX- pair), you reduce EMI emissions because the wire pairs help to cancel external transmissions.Since RS422/RS485 are truly differential for both TX and RX, cable distances can be much longer and data rates much higher than RS232.the RX422 TX+ pin would drive 5V for "high" (which is valid RS232) and 0V for "low" (which is not a valid RS232 signal level).the RS422 TX- pin to be held at GND and.Attempting to do this (by connecting RS422 TX+ to RS232 RX and RS422 TX- to RS232 GND) would cause.Since the TX pair of wires does not have a GND wire, RS422/RS485 can not be connected directly to an RS232 port.4 wires are needed for a data only serial channel: TX+, TX-, RX+ and RX.RS422 RX+ and RX- detect differential voltages just as in the RS423 case.

TX- is not tied to GND as in RS423, instead it drives "opposite" the voltage that is on the TX+ pin.TX+ to 5V and TX- to 0V for a "high", or.The TX pair of wires TX+ and TX- either drive.The voltage levels of signaling is +5V for a "high" and -5V for a "low", which is within the RS232 voltage level ranges mentioned above.TX- (GND) just ties to the RS232 GND pin and provides a common GND.The single ended TX+ pin drives the RX pin of an RS232 port.4 wires are needed for a data-only serial channel: TX+, TX- (GND), RX+ and RX.

RX is comprised of RX+ and RX-, which go into a true differential receiver.TX+, a single ended signal, and TX- (which is really just GND).RS423 uses single ended TX and differential RX.The voltage ranges of RS232 signaling is +3V to +15V for a "high" and -3V to -15V for a "low".Disadvantages of single ended signaling is that it is more susceptible to noise than differential signaling, effective cable distances are shorter and data rates are slower.Only 3 wires are needed for a data-only serial channel: TX, RX, and GND.This means a common ground wire is shared between TX and RX. What are the differences between the different serial protocols, RS232, RS423, RS422 and RS485?