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

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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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64 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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61 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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52 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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32 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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49 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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83 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
182 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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2answers
95 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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173 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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2answers
399 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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3answers
85 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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122 views

MODBUS WRITE COIL opearation

I am trying to perform write coil operation.In below code i can read data But i could not able to performs write operation. SInce my code size is big i am pasting part of code. Give me simple example ...
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251 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
110 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
271 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
123 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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90 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
770 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
115 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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121 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
288 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
117 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
434 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
592 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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2answers
101 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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135 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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107 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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2answers
145 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 ...
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223 views

ModBus RTU and ASCII exclusively in one RTU

Having a device RS-485 that can be set in two modes: ASCII and Modbus RTU. With ASCII I get full functionality of the device, with Modbus only a few registers are available. Which are the exact ...
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2answers
243 views

Networking options for multi-node Star topology

I want to create simple network consisting of 1 master and up to 16 slave nodes. Project will be based on PIC MCUs. Network has the following specs/requirements: Relatively low speed Inexpensive ...
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2answers
318 views

RS485 signal transmission

I'm trying to build large LED panels (3x128 LED modules) using WS2801 LEDs, with data coming from a Teensy 3.0 microcontroller. I'm having difficulties transmitting my Data and Clock signals between ...
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79 views

RS-232 <-> RS-485 converter with special wakeup pin

I need am RS-232 to RS-485 converter with a special pin for waking up the RS-485 master. Effectively this means that in addition to standard (2-wire, half duplex) RS-485, I need two more wires ...
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190 views

How do I wire a 9 pin serial connection to an Arduino?

My question is pretty straightforward. I've got a big old machine that has an RS-485 connection on the back and I've got a converter from RS-485 to 9 pin serial. The device I'm connecting to sends ...
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2answers
178 views

RS232 hotplugging

I've noticed that when I connect/disconnect the RS232 cable to my micro-controller, I receive a garbage character at the other end (my pc). Is there a way to prevent this? I want to eventually move ...
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2answers
157 views

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 ...
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1answer
283 views

What is 1/8 unit load in RS485 communication?

Something I saw is 1/8 unit load. In that document, it states that RS485 will allow up to 256 transceivers on the bus by using 1/8 unit load. My question is, what is 1/8 unit load and how do I use it? ...
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4answers
540 views

variable-speed focus PTZ protocol

I'm building camera systems to mount on top of a TV tower. When storm clouds roll, in the video is displayed on the TV weather report. No one wants to climb the tower to manually pan and tilt and zoom ...
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118 views

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 ...
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1answer
462 views

How to Control SM1 Inverter Drive Frequency with Arduino?

I am back at trying to control the frequency of an SM1 AC inverter drive due to the fact that I never got it going the first time. However, this time I would like to use an Arduino. The manual for the ...
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196 views

Different RS485 Full-Duplex with RS422

Are RS485 Full-Duplex interface same with RS422 interface?
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1answer
341 views

Faulty RS-485 device has irregular effect on neighboring devices in bus setup

I am trying to understand the mystery of how one faulty RS-485 transceiver, in a network bus with several devices, seems to have very irregular influence on its own and its neighbors transmission ...
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3answers
1k views

Serial bus Raspberry Pi to multiple AVRs

Background: I'm trying to replace the electronics for a ice hockey scoreboard. The old electronics had the following issues: It stop working. I have since discovered that a couple of diodes and ...
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4answers
1k views

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 ...
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2answers
1k views

How to de-couple DMX512 with opto-isolators?

I'd like to build a DMX512 device. The problem I have is how to decouple the device from the bus. I decided to use opto-isolators, but how should I wire the diode part of the isolator? Since I need ...
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1answer
535 views

J1708 Half Duplex Collision Detection

SAE J1708 is basically an RS485 hardware interface without the typical 120 ohm termination resistors. In typical applications, a half-duplex RS485 transceiver chip is used to connect to the bus. In ...
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765 views

Pull-down resistor with ADM485

I have ADM485 already mounted and an output of some device, buffered by CD4050BM. For the circuit to be safe for the RS485 bus, the ADM transiver initially should either be in Z-state or read-state. ...
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2answers
812 views

No response from device when using rs485

I've been stuck on this issue for quite some time. I am trying to use an arduino to communicate with another device using RS485. The problem is that I can see the data being sent but, the device does ...
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1answer
351 views

Unable to communicate with a deice over rs485 [duplicate]

Possible Duplicate: No response from device when using rs485 I've been stuck on this issue for quite some time. I am trying to use an arduino to communicate with another device using RS485. ...
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1answer
321 views

What serial signalling format is this? (RS-485?)

This is a mystery signaling standard that I'm trying to sort out. It looks more or less like RS-485 to me, but I don't recognize the long looking start bit, and the "idle" state of the line looks a ...