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Questions tagged [rs485]

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

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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 ...
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RS485 Protocol Reverse Engineering & Replay Challenges

I'm trying to reverse engineer the RS485 protocol used by my home heater/AC. This protocol handles communications between the wired remote control (WRC)/thermostat and the main heater/ac indoor unit (...
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Replacing the physical layer of MIL-STD-1553 with RS-485

I've been reading about MIL-STD-1553 buses, which very briefly are multidrop Manchester-encoded 1 Mbit/sec 32-station: a single "bus controller" master and multiple "bus terminals" slaves which speak ...
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RFI protection for a stepper motor controller

I'm building a remote tuning device for a magnetic loop antenna. It will use a stepper motor to turn the shaft on the mag loop's variable capacitor. The electronics will consist primarily of a ...
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Implications of using a 2C-#18 twisted shield pair nec type cmr cable for RS-485

The cable will be passing modbus and another equal cable will be used for loadshare. The total cable distance will be about 100ft. Its catalog number E2032S. I notice other threads related to CAT5, ...
wouldliketoknow's user avatar
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rs485/modbus issue

I am trying to enable modbus RTU communication between 2 inverters. Both are set up with unique IDs, 9600Hz, 1 stop bit, No parity bit. I can communicate with 1 at a time, as shown below in the ...
fruit salad's user avatar
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Reason to have MSB in a serial communication always high

I'm working on a code (written by other people) that uses a custom protocol to transmit data over RS485 in 8-bit packets. For some reason, the protocol is built so that every 8 bits transmitted are ...
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Serial circuit protection design

I've been researching RS485 hotplug protection for a while and come up with the following solution. The reason is that I burned two custom Arduinos, after further investigation it turned out the GND ...
Maciej Swic's user avatar
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Which instructions do I use to be able to use UART directly on my STM32F107 microcontroller?

I've tried to figure this out on my own but after almost a week I'm still at more or less the same place where I started. So, I have an STM32F107 microcontroller on a board, which is linked to another ...
DexTr's user avatar
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Isolated RS485 without specialized IC

I'm looking for replacement for ADM2587E. This is ADM2587E: Can I just use cheap, not isolated RS485 transceiver like MAX485 connected to microcontroller TX, RX, DE/_RE via optocouplers and power it ...
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RS485 registers for calculating total power consumption (kwh)

I have an energy meter (OHIO A2000) which has been now discontinued by the manufacturer. Anyway, I'm following the manual for extracting energy parameters through Modbus RS485 communication. I'm ...
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RS485 ground noise problem

I'm using the USB FTDI dongle to convert USB to RS485, half duplex, 3 wires (A+, B-, GND) with 115200 baud rate. I'm working with controller of NXP (K64) and I'm experiencing random tx enables on the ...
roy.me's user avatar
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Relay+SMPS = Noise in RS-485 bus

I designed a board with a microcontroller (Atmega328), 3 relays and a RS485 transceiver. The relays control SMPS LED drivers (Meanwell LPF series). The system consists of 10 boards, each one ...
Bulcheter's user avatar
2 votes
1 answer
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Cable shielding groundloop

I am trying to connect a encoder to a motor controller which runs very close to the motor that it controls (30+ amps). Due to the risk of high EMI of the motor inducing on the encoder signals, we send ...
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How to connect RS-422 to 2× RS-485?

I want to connect two Arduinos via RS-422. I have 1 converter RS-422 to TTL and two RS-485 to TTL. How I can connect outputs of my converters (Y,Z,B,A on MAX490 and A,B on MAX485)?
Рома Рома's user avatar
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RS485 isolated or not for home automation system?

I'm creating a home automation system for condominiums. Practically there are a series of control units that communicate with remote sensors. Communication takes place via RS485 serial on an Ethernet ...
Federico Massimi's user avatar
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Why is my voltage disapearing from esp32 to RJ45 connector?

I am working on a project where I am sending data from an ESP32 through an RJ45 cable to a DMX decoder. As far as I can tell my wiring is correct, however, I do not appear to be getting the signal to ...
Paul Carlson's user avatar
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1 answer
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What is the operation of this RS485 transceiver having this connection?

I am confuse with the R1 and R2 function. The "Direct Connection" wire is connected to another transceiver's DE/RE. When the DE/RE is high, driver is enabled, and when the DE/RE is low, the ...
yessi's user avatar
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How to reduce noise on RS485 line?

The above picture is the output of a MAX485 IC, which is an RS485 transceiver. When the Cable comes near an AC power line, this kind of noise adds up. Without the presence of the AC main line, its ...
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What are the correct signal ground connections in an RS485 system with a shared ground on motor drivers?

I'm in the process of designing a motion control system using RS485 and whilst we've generally made things work in the past with a more trial and error approach, in the interest of doing things right ...
Will Laslett's user avatar
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Connecting 12 V RS485 appliance (soil sensor) to USB 5 V RS485 adaptor

I have a 12 V RS485 appliance that measures some soil resistance etc. It is a 7-in-one soil sensor, the 12 V version of the 5 V version shown in the link. I could not find a 12 V USB to RS485 adaptor ...
Allan Teo's user avatar
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Fault Protected RS485 circuit

I am designing a product for use in the industry and it needs to include a fault protected RS485 interface. In the industry the most normal voltage for the power supplies in the machinery is 24V, but ...
abomin3v3l's user avatar
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Atmega328 and max485 schematic problem

i'm making atmega328 and max485esa in one pcb. first build using an external 5v dc source and without any problems. the code works fine, the ws2812 led on the receiver module can light up. the second ...
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How to create an RS485-compatible line driver with an adjustable slew rate?

I need to make an RS485 compatible line driver, capable of 12Mbit/s with fast slew rate, but with the capability to reduce the slew rate to about 50ns rise/fall time when operating at lower bitrates. ...
Timmy Brolin's user avatar
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Need Help Connecting Arduino to PC via RS485 with Max485 breakout board

I am currently attempting to connect an arduino to a PC via the RS485 communication protocol using a max485 to convert the RS485 to serial. It does not however appear to be receiving any data at all. ...
Patrick Voorhoeve's user avatar
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How to test for PCB ground being pulled up to 2V when connected to RS485

I am currently trying to find an easy way test to diagnose a problem on some of our PCBs where the ground of the PCB is being pulled up to 2V's. The Board Simple modular RS485 sensor board. The main ...
Oli's user avatar
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How to interface a Raspberry Pi Pico to DMX / RDM

Years ago, I was looking at creating a stage DMX controller using AVR. Time moved on and the Raspberry Pi Pico has now been released. I'd like to revisit the project using a Raspberry Pi Pico, which ...
AJ.'s user avatar
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The Best Place for the Reverse Polarity Protection Diode

I have several RS485 devices. All of them are connected together and power by a 12V power supply. Each device has its own 5V voltage regulator. I want to use diodes for each of them to protect aginst ...
Vahid's user avatar
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Transmission lines in paralell for RS485

I have a system with two RS485 transceivers connected by a 300 meters long cable, with 6 wires inside it. In this case, 3 paralell wires of this cable are being used for the "A" signal and ...
Victor de Luca 's user avatar
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RS485 communication issue

I have used PIC18F45k40 device for RS485 communication. I have 2 ckts one is isolated and another non isolated RS485 design. I have schematic & placement for reference. I have connected multiple ...
Ajit N's user avatar
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How are DC offset square wave transmission waveforms generated?

The balanced serial transmission shown in the picture is similar to rs485 except that the square wave has a DC offset (e.g. 24VDC) with an alternating offset. The transceiver chip "drives" ...
MandoMando's user avatar
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MAX487 can transmit but won't receive

I am trying to use a MAX487 chip to convert a regular UART signal to half-duplex RS485 signal and vice versa. I am using Atmega328PB as my micro controller. My circuit has no problem with transmission,...
HumbleBumble's user avatar
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RS-485 device to RS-232 adapter MUXing not working as expected

I have a RS-485 device that returns serial ASCII constantly. As the device might near very high voltage or electromagnetic areas, I need to ensure the RS-485 to RS-232 adapters I've been supplied with ...
ChrisAdmin's user avatar
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6k views

RS485 Pull-up, Pull-down and single termination resistor

Currently I use for Modbus RTU via RS485 with a shielded cable length of about 5 meters and a bitrate of 19.200 bit/s. Wired are 680 Ohm pull-up (A->+5V) and pull-down (B->GND) resistors near to the ...
wenzul's user avatar
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Providing RS-485 ground when no pin is provided

I have a PC with an RS-232 to RS-485 converter controlling (@ 9600 baud) a large piece of HVAC equipment in an adjacent utility room, <50' away. We are adding two more of these pieces of equipment,...
Peedygasser's user avatar
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52 views

PCB Power Divider Tee for RS 485

For a RS-485 Communication using a Maxim MAX3292 Driver, Full Duplex, 1/4 load unit (54 \$\Omega\$), 5 Mbps, with UTP 120 \$\Omega\$, standard cable, for each receiving unit I am thinking on a design ...
Brethlosze's user avatar
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2 answers
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SPI with differential line drivers, and star configuration problem

Folks I am helping to design a circuit for a group that uses the odrive motor driver board. The odrive drives two brushless motors and the MCU uses SPI to connect to motor encoders. People using the ...
Owen White's user avatar
1 vote
0 answers
71 views

Signal Attenuation TVS and series resistor

This question is in regards to signal attenuation on high speed data lines like RS-485 (and any others as well). I'm new to the signal world, so please bear with me here. Are there some useful ...
Chance-the-Gardener's user avatar
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Addressable RS485

I have a requirement to take a board that interfaced with RS232 and put it on a half duplex RS485 bus. The obvious problem is that at the very least the board firmware will need to be altered to be ...
Dirk Bruere's user avatar
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Problem with Pyserial read time

I'm building a RS485 network with rpi3 as master and a bunch of c51 mcu as slaves. After sending an address, the master waits for the slave to respond and then starts to send data. I'm using Pyserial ...
gordon's user avatar
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RS485 transmission errors

I am trying to get two Atmega328ps to talk to each other over RS485 with MAX485 as transceiver. Below is the scope trace of D+ and D-. Yellow : 485A line, Cyan : 485B line, Blue: A - B (...
beta_male's user avatar
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For wrong termination resistor uses

Over 485-interface slaves are connected as multi drop, physically daisy chain. Those have built-in termination resistor, and the value is 120 ohm and no select switch for termination on/off. So it ...
Aveugles's user avatar
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Using same DB9 port for RS232 and RS485 (selectable) - looking for IC

Do any of you know of any transceiver ICs that can switch between RS232 and full or half duplex RS485? I'd like to be able to select which type of communication is used with either a jumper or input ...
Pugz's user avatar
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Difference between Echelon TPT/XF and RS485 transceivers

We are going to connect to a LonWorks network and all devices connected to network have TP/XF-78 transceiver. Can anyone describe the difference between the two?
BHP's user avatar
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ATTINY85-20SUR and serial communication

I am trying to use this chip ATtiny85 for serial communication. So my question is, would you recommend using it for serial communication, such as storing names, IDs, data, and last operations? Should ...
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Replacing MAX485ESA IC into a RS485 module but not working

I have been struggling a lot with a MAX485ESA IC I bought from aliexpress. What I want to do is replace the component from a rs485 module. For some reason they don´t work and I was wondering if anyone ...
user2808169's user avatar
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1 answer
160 views

Connecting a non-galvanic isolated RS-485

I would like to consult if I am designing RS-485 connection correctly without risk of damaging anything. Main goal: I want to get data (e.g. flow temp) from Danfoss ECL 210 district heating control ...
Janis P's user avatar
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How fast can a Schmitt trigger operate? Can I use it for signal conditioning digital serial data?

I would like to know if I could use a Schmitt trigger chip (e.g., 74HCT14, CD40106B and 74AC14) to clean a 12MHz serial digital signal that has gone through a long cable and will pass through multiple ...
Emerson's user avatar
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Potential Reasons for Fault on RS-485 Transceiver

I am working with the MAX3441 RS-485 transceiver, but I have run into faults with the three transceivers I have tested, so I am wondering if anyone can shed some insight on potential reasons for the ...
SubjectFocused's user avatar
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Problem with Max 485 RS485 to TTL chip (Not Receiving Data)

I am working on a project connecting Arduino UNO r3 and an RS485 modbus master with MAX485. The connections are shown below. ...
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