Electrical Engineering Stack Exchange
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Questions tagged [rs485]

EIA RS-485 is a serial communication standard using differential signaling.

Further reading:

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What does 232 signify in the RS232 standard?

"RS" in communication standards RS232 and RS485 stands for "Recommended Standard". But what information does "232" or "422" or "485" convey in the name? What naming convention is used for numbers succeeding the letters "RS" when naming the RS…
Sonam
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Is CAT5 cable good enough for RS-485 vs "true" RS-485 cable

I have a serial comms project coming up. A number of boards with RS-485 interfaces need to communicate. Date rate is 57600bps and cable length will be less than a few hundred feet. Will shielded CAT5 cable work well enough in this situation or…
SeanLabs
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RS485 network ground pin - when to connect?

As many know, one can implement a simple node to node rs485 communication by using only two wires, A and B. Well, the standard specify to connect the ground of the two node together. from Wikipedia: In addition to the A and B connections, the EIA…
fhlb
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Significant differences between CAN and RS485 regarding the physical layer

In comparing the physical layer of CAN and RS485, I am trying to find the advantages of either one over the other. I found out that they are quite similar. Both are good in terms of common mode rejection and both need protection against ESD and…
Macit
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At what cable lengths are termination resistors required for RS-485 networks?

I've noticed my experiments in the lab with RS-485 work fine with fairly short cables, but termination resistors are needed for true installations. Is their presence or absence a function of the cable length, or other factors?
fred basset
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The origin of the "cable length - data rate" graph in the RS-485

In several RS-485 application notes one can find a graph that describes the relationship between data rate and cable length, like this one: But not a single document describes how to calculate it on your own correctly. It must depend on several…
Looongcat
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RS-485 shield and ground wiring practice

After some reading I was convinced that I have three options: The best: connect A and B lines to a twisted pair, signal ground (SG) line to therd wire in the cable (or to a second twisted pair) and connect cable shield to protection ground (PG)…
Roman Matveev
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RS485 termination: AC + failsafe + parallel + bidirectional

Knowing that I need to refine my RS485 circuitry, I've been reading. I have a series of specific questions and I hope that you'll indulge me as I describe how I attempted to follow through an application note. Here are some basics of the serial comm…
Reinderien
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Correctly using RE and DE with RS485

I'm trying to build a RS-485 project using MAX485's. However, I'm having trouble finding out how to correctly use the RE and DE pins. Some PDF's and websites say that RE and DE should be tied together and then connected to a pin on a microcontroller…
user9993
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Running CAN bus with RS-485 transceiver

Recently I had a discussion whether one could use RS-485 transceivers for a CAN-bus network in order to gain the flexibility to use the same hardware either in a CAN-environment or in half-duplex RS-485 network, albeit with different software.…
Arne
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What protocol is this waveform?

I'm trying to reverse engineer a communication line between two components. However for debugging I'm connecting to only one of them, powering it up and looking at the signal. I have no experience with this so I'm really stumbling around with some…
AntoineG
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RS485 minimum node spacing - 3 x RS485 device on PCB

I would like to ask something about RS485 minimum node spacing which is described in (Page 5) TI Design guide I would like to create device which consists from 3 existing RS485 devices. My plan was that I put these 3 devices together on single 2…
Wojtkingson
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RS485 terminating resistor power rating

As far as i know rs485 specifies a bus common mode voltage of: -7V to +12V the terminating resistor is 120ohm , using VxV/R , yields high power rating to the resistor , certainly more than 1w . (12x12/120 =1.2w) However looking at many products and…
ElectronS
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How to find the UART line is free for send data

I have several boards that communicate together with Rs485. They have ATMega series microcontrollers such as atmega168p or atmega8. Each board is free to send data at any time and I have limitation that lead to I Cant use Modbus. The number of…
Ali
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Any good way to automatically enable an RS-485 transmitter in hardware?

Does anyone know of a good circuit that would automatically enable the transmit on an RS-485 driver when characters are transmitted? In our designs we currently use RTS to drive the driver transmit pin, but then the RTS signalling has to be done in…
fred basset
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