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

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Home automation on Cat5e again: is this a reasonable multidrop protocol?

Previously I have asked about running I2C over CAN PHY over Cat5e cables for my home automation project. Now after a round of money saving and experimenting, it seem to me that abusing RS485 chip ...
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60 views

UART Interrupt won't work

I have a problem when trying to test send and receive lines on RS485 communication, anyone know what may cause a problem here? It works without interrupt but with interrupt won't work. I am working on ...
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62 views

How to test RS485 communication via PC terminal?

I've tested RS232 communication via terminal with LPC1788 ARM CPU, and it works, now I want to test RS485. I just want to make simple echo program, what is sent, that is returned. Problem is that CTS ...
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47 views

Is it safer to use multiple RS-485 point to point connections compared to a daisy chain?

When wiring multiple RS485 slaves to a master equipped with a RS232/RS422/RS485 interface*: is it safer to wire multiple point to point connections from the hub with their own termination resistor, ...
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99 views

Can I an RS422 interface to Arduino's serial pins?

I have a custom-designed circuit that communicates to and from the external world through an RS422 interface. I wish to communicate with it with an Arduino, preferably UNO. The RS422, much like the ...
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33 views

PIC32MX with RS485 not working while receiving?

I have to interface PIC32MX150F128B with MAX485. The transmission part had done well by shorting RE and DE, and giving it a high pulse during transmission. DI being connected to TX pin of PIC. But ...
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57 views

Using RS-485 receiver with RS-422 signals

I have a controller that has a RS-422 output, can I use it to only send data to another device that has RS-485? please explain Thank You!
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58 views

Multipoint Ethernet cable as an RS485 data bus

How can I create multipoint connections with an Ethernet cable an retain the high reliability / low noise achieved by the wires being twisted in couples? I think I need to create Faraday cage, but I ...
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57 views

USB to RS485 converter: Auto enable control

I have been trying to program infineon mcu via usb to rs485 converter. Procedure to check mcu is working fine: Query command sent using hercules : 0x80 Response sent by mcu : 0x55 (correct response) ...
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136 views

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 ...
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39 views

when to cascade Modbus TCP/RS-485 gateways?

I've noticed that many Modbus Gateways support cascading. Cascading makes sense, when converting from TCP to RS-232 since RS-232 allows 1 transmitter/receiver on each line. But does it make sense ...
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88 views

Looking for a long-distance (~1km) physical layer

First of all, I have to say my knowledge on how networks work physically is limited. I am working on a project to interconnect farming equipment over fairly long distances, at a maximum of 1km, more ...
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154 views

PIC24F UART Rx Interrupt not firing

I am currently trying to write code for a 48 channel DMX controlled dimmer using a PIC24FJ32GA002. Using a scope I have confirmed that there is a DMX signal reaching the Rx pin of the UART which has ...
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162 views

What kind of component would I need to put a break in a RS-485 bus?

I'd like to have some kind of electronically controlled switch (transistor, relay, solid-state relay, etc) that acts as a break in a RS-485 bus. The effect I would like is to optionally split the bus ...
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1answer
60 views

rs485 loading problem

I've one system with rs485 with max485 chip with microcontroller (pin 2& 3 r connected to gpio).To access that system I've made one other system with ilx485 chip. Pins 2 & 3 of these are ...
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104 views

Wiring RS485/422 to RS232 converter to a given device pins [closed]

I'm trying to establish a full-duplex and then a half duplex communication and need to wire a device output to an RS485/422 to RS232 converter. Here is the device output pins for full and half ...
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1answer
259 views

Looking at a RS485 signal with an ocilloscope

Is it possible to view a RS 485 diffential signal using a Rigol DS1102E 100MHz Digital Oscilloscope, Dual Analog Channels, 1 GSa/s Sampling, USB Storage? I can see a signal that looks more like ...
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131 views

Short distance star topology, no terminating resistors on RS-485 network

I have an application with one master and 4 peripheral devices on a single RS-485 bus with maximum distance from master to device less than 1 m and maximum bandwidth of 115.2 kbaud. Remote devices are ...
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79 views

RS485 half duplex communication issue

I have a London MR400s taximeter and I wanted to communicate with it so I have connected it with my PC using RS485 half duplex cable. I am using termite terminal for polling and receiving the data. ...
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2answers
199 views

RS-485 isolation required?

I would like to confirm my understanding. Suppose I'm want to have two battery-powered MCUs inside an (unmanned) aircraft communicate with each other via RS-485. If those MCUs are powered from the ...
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251 views

Connection problem with RS485 system on PC with RS232 port

I am developing a system in which I have to integrate hardware. I am from computer background, so I don't have much knowledge about hardware systems. The issue is I have to integrate with London ...
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1answer
169 views

DMX512 packet issue (no break?)

I'm not sure if I'm reading this wrong or something, but this is a trace of the DMX packet that's coming from my USB-RS485 module then being converter to UART logic levels for my microcontroller. ...
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1answer
453 views

Raspberry PI's SPI over RS485

I'm trying to understand how to connect a SPI device (a mifare RC522 RFID board) over long distance to my RPi via SPI. I searched and find I could connect those via SPI over RS485 using a MAX490. ...
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163 views

How can we sure about common mode voltage for RS422/RS485 without ground connection?

RS422 and RS485 standards specify different common mode voltage limits. In some application notes, I see that ground connection between two node is somehow optional. Suppose that two nodes are ...
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341 views

RS485 network failing on replacing SP485 chip with MAX485

I have created an RS485 communication network as shown below. {PC}->[FT232->RS485](120 ohm)<----twisted pair(2 wires)------>(120 ohm)[RS485 -> MSP430] Here PC acts as Master and sends the data ...
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145 views

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 ...
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61 views

75176B running very hot

I'm using this chip to drive DMX as is common. With no differential load/receiver load it gets hotter than is comfortable to touch, and with a receiver, still warm but not so hot. The circuit is very ...
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107 views

RS-485 connection problem

I have device connected to Moxa 5232 serial server via 2 wire - RS485. I use Modbus RTU protocol. driver -(rs485)->Moxa 5232 --(Ethernet)-> PC I have a correct signal on transmitting lines (my ...
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176 views

Full Duplex RS485 recommendations

I am looking at a few IC's for full-duplex RS485 communication. Are there any recommendations? The current options I am looking at are: SP490 SN75179 LTC490 The first two are well priced for my ...
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1answer
465 views

Why does FTDI RS485 signal look wrong?

I have an in-house board with a microcontroller (Microchip dsPIC33E) and an RS485 driver (Analog Devices ADM2587E) that I'm trying to connect to a desktop PC using an FTDI (USB-RS485-WE-1800-BT) USB ...
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308 views

Connectors for a RS485 multipoint bus

I need to connect a bunch of Mass Flow Controllers on a RS485 (TIA-485-A) multipoint bus. I will use Modbus protocol to communicate with the devices. As specified on modbus.org (Specification and ...
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393 views

RS485 with ST Nucleo, not sending any data

I'm trying to communicate with an energy meter (MODBUS protocol) using ST Nuceleo F401RE via MAXIM MAX485 chip. I'm unable to receive any data from the energy meter. I can confirm that all my hardware ...
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1k views

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 ...
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193 views

Biasing resistors for RS485

I know I should have a terminating resistor but do I need biasing resistors on the +/- lines of an RS485 differential signal?
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500 views

MicroC rs-485, pic16f887 String sending problems

How can I send the string "test" from a master pic to a slave? I'm using MicroC RS-485 library example: http://www.mikroe.com/download/eng/documents/compilers/mikroc/pro/pic/help/rs-485_library.htm ...
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181 views

Cannot establish serial communication from a sensor

I have the following wind sensor (RT240): http://www.nrgsystems.com/FileLibrary/829de7ea934944f09798ad2830abfa65/RT240_and_RT20_Manual.pdf It has a 8 pin connection cable and I'm trying to ...
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822 views

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 ...
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1answer
535 views

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) ...
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137 views

Digital potentiometer analogue for high voltages

I have an RS-485-like (not a standard RS-485, but close to it) circuit with 35V+ voltages in it. I need to change resistance of the resistor, that installed parallel to my device data connectors A and ...
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1answer
2k views

DMX on Arduino with RS485

I'm implementing DMX on Arduino. DMX uses the RS485 standard to communicate. In the specifications of RS485 it notes that there is a positive line, a negative line and a ground line. If the positive ...
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1answer
178 views

Connecting 4 devices on RS232

I have two PCs (very old, without usb but rs232 port) that talks via RS232. They send to each other very small bit of info ( one character every 10sec). Now I need to connect additionally two sensors ...
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194 views

What is the rs-485 protocol for controlling old flipdot displays?

I have an old Luminator flipdot 16x112 pixel bus destination sign I'd like to hack. There are numerous resources on the internet for controlling the flipdot display panels with new circuitry, ...
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1answer
687 views

RS-422 distance sensor with arduino

I need to make a converter to go from RS422 full duplex to my Arduino. I have found lots of different chips which I think can do this, but am slightly confused by the terminology. The RS422 device is ...
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2answers
262 views

RS485 + Power over twisted pairs, still need isolation?

I need to communicate with a piece of hardware on an elevator car. I have a few twisted copper pairs available, but it's not CAT5, so Ethernet is out. Instead I'd like to use RS485. I've been ...
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1answer
900 views

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 ...
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1answer
1k views

atmega32 communicating using rs-485 modbus protocol

I am trying to read values from a meter (WDM303FDWA1) through ATmega32. The communication to the meter has to be done by RS-485 modbus protocol. I would like to know what IC do I have to use to ...
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134 views

How to “auto-disconnect” from rs485 bus when power off

I have many devices on a RS485 bus. When I disconnect power from one device, the rest of the (powered-on) devices seem to communicate with each other just fine. At least it seems to be working today. ...
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177 views

RS-485 / CAN signal levels

From what I know, CAN at the physical layer in the "recessive" state just lets pull-up/pull-down do the work. Does that mean the rise time is theoretical slower than a RS-485 transceiver? And about ...
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122 views

Connecting RS-485 devices transparently

I have a main computer that has a RS-485 board. It communicates with its sub systems via this comminication board. I have also a test computer thas connected to main board via RS-485 channel. It will ...
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198 views

What microcontrollers can utilize 30-52MBit RS-485?

I am rather new with micro controllers, please, push me in the right direction. I'm planning to use RS-485 network for audio streaming at home. On maxim-integrated site there are drivers, which have ...