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

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Different wave form of Rs485

I have a device in aircraft (DEU). It has a output data to control a light ( diming control). In accordance with aircraft document this data is rs485. But i see a different form of wave in ...
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50 views

msp430 DMA UART for Modbus

I am using MSP430 UART with DMA transfer for sending Modbus packets. As a master at the end of packer I need to change my RS 485 transceiver direction line for reception. I am sending 10 bytes in ...
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26 views

IC Thermal shutdown recovery time

Many RS485 transceiver chips have a thermal shutdown when the junction exceeds 150C. Typically they switch back on once the junction temperature drops 15 degrees. How long does that typically take? ...
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83 views

What is the relationship between DMX and RS485? Are there any breaks in the protocol in relation to one another?

As far as the DMX is RS485 and at what points one moves away from the other? breaking the standard/protocol?
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1answer
79 views

Likely RS-485 color coding of three wires?

We received a piece of equipment (actually from an Italian manufacturer, if that gives a hint) which uses RS-485. So, as well as a power connection the devices have THREE WIRES (bare wires) coming ...
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58 views

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 ...
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1answer
137 views

Serial Communication with rs232/485 and rj45

I am working a project where I want to connect and control, using Labview, TDK-Lambda Power Supply Process Vacuum Controller Ion Gauge (MODBUS interface) They both have rs232/rs485 capabilities, ...
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1answer
56 views

RS485 selectable termination device

I was given the task to make a new version of a board which have this little contraption for RS485 termination resistors: simulate this circuit – Schematic created using CircuitLab My ...
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2answers
125 views

RS-485 Modbus device to MCU

I have a device (an energy meter) that sends data via RS-485 (Modbus protocol). And I want to collect it with MCU. The important thing is that I'm trying to design a board and I want it to be ...
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95 views

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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1answer
104 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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208 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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59 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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2answers
369 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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57 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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2answers
86 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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73 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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75 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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3answers
343 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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52 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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2answers
95 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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2answers
291 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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4answers
187 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
79 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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1answer
166 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 ...
2
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1answer
434 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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167 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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93 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
381 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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1answer
390 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 ...
3
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1answer
229 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. ...
0
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1answer
658 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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2answers
190 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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422 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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164 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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71 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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1answer
207 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
576 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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447 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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454 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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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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3answers
260 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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1answer
639 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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2answers
213 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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2answers
1k 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
766 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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1answer
149 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
228 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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239 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, ...