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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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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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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RS485 Common Ground: Common Voltage or Common Wire or Both?

RS485 connection needs a common ground, but I am very fuzzy about how that works over longer distances and more complex systems. When the transmitter and receiver are about 1000m apart, there will be a voltage drop so the receiver won't have the…
Arthur Tarasov
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RS485 implementation problem

I'm trying to implement RS485 link between mcu and pc. I'm using MAX485 for testing my setup. Question: I can not receive bytes if I use termination resistor. Why? How to solve this? History: If I place a termination resistor (120 ohm), it is…
ceremcem
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Standard pinouts for RS485_interface

Is there any standard DB9 pinout for the RS485 interface? If so please share the same.
Chitharanjan
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RS-485 Stub Connection Best Practices

I have a system with an RS-485 bus master and up to 12 slaves. The master and slaves are located in different assemblies and are connected with an RS-485 bus that is inside a cable harness. The cable harness also provides power and other comms. The…
Scottlysan
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Is it OK to use RS485 with separate wires for each device?

I know common use of RS485 is top wiring diagram. But in my project we need to use RS485 for extend range and reliability connection but connection will be bottom wiring diagram. Can I use a single RS485 transceiver IC? Are there any problems with…
Sum Settavut
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RS485 entering and leaving a PCB

For architectural reasons, we have a need to take a twisted pair (of an RS485 bus) into a PCB and then out. The PCB traces would add about 2 cm (just less than an inch) of length to the bus. The stubs connected to this differential trace pair in the…
benHur
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Hijack/observe RS485 communication data by wire tapping?

I have some Computer -> LED Matrix Screens system like this diagram: ---------------------------------------- RS485 (A / TxD- / RxD-) COMP > | | | | | SERVER --------------------------------------- …
c2h2
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RS485 Node/Cable Testing/Simulation

I am designing a system using RS485. There will be >100 nodes on a bus, each with input and output connectors, separated by ~1m. In order to determine the signal quality at various speeds, I would like to make low-cost nodes that behave electrically…
jfowkes
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What is the best practices of placing of termination resistor

Usually I placed the 120 Ohm termination resistor pads in the PCB. So I could place the resistor or not during the PCB assembly for different applications. However I suppose that the termination resistors should be a part of the transmission line -…
Roman Matveev
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sn75176b vs max485 price for DMX

Quick question - I'm using a RS485 transceiver for transmit only, and for a SIOC8 part there are two commonly used I've seen on the internets: MAX485 @ (£)1.83 & SN75176BD @ 0.271 and there's ADM4852ARZ @1.67 (lowest qtys to compare) Most specs…
LightTrepidation
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RS485 voltage levels

During RS485 transmission, what is the absolute voltage change in the TXD+ and TXD- pins in RS485? Do they swap value (IE if TXD+ is sitting at 4V quiescent, then it goes 4v 0v 4v during transmittion) or do they just move "differentially" (IE TXD+…
GreenAsJade
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How a PC with an RS232 port read serial data coming from a device with an RS-485 output?

We have a program in Windows OS which is capable of reading serial data from an RS232 port or USB ports. We have a device which is only using RS485 communication (2 wire-half duplex). Is there a way to use DB9 cable for reading data or should we…
user16307
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Can I use devices with different unit loads on the same bus? If not, why?

I've been having trouble getting a rs485 communications bus working with some external devices. I have an Arduino hooked up to a MAX487ECSA+ which goes through some cabling to my devices. Using an oscilloscope, I can see the signal (with sufficient…
Andre
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