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

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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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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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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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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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58 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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55 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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213 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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57 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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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
93 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
43 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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98 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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285 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
76 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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1answer
100 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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92 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
114 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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116 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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162 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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218 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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67 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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156 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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123 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
134 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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148 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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328 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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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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350 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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138 views

Different RS485 Full-Duplex with RS422

Are RS485 Full-Duplex interface same with RS422 interface?
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269 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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861 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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678 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
886 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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367 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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571 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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621 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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291 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
294 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 ...
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1answer
295 views

DMX512 Remote controlled LED

I'm having a problem with this circuit. I am trying to get an LED wash light circuit to be remote controlled via DMX512. The problem is, after I designed the circuit for the RS485 (which will deliver ...
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Arduino as modbus master with MAX485 doesn't get any response

I'm having some troubles trying to query a modbus slave with an Arduino through RS485. I've already succeeded in querying a software modbus slave running on my PC through the USB/COM port using the ...
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Different behavior of FTDI USB RS485 on different computers

I use a FTDI USB-RS485 adapter cable to connect a RS-485 device to a computer. The communication is fairly simple, the computer sends periodic requests, the device answers them. On one computer ...
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Framing error on Rx line in rs485 to ethernet converter [duplicate]

Possible Duplicate: Framing error on Rx line in rs485 to ethernet converter I have a device connected to MOXA nPort 5150 via 4-wire rs-485 cable. Termination resistor inside the converter ...
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1answer
342 views

Framing error on Rx line in rs485 to ethernet converter

I have a device connected to MOXA nPort 5150 via 4-wire rs-485 cable. Termination resistor inside the converter was set to 1 kΩ (another option was 150 kΩ, which didn't work at all - I got framing ...
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2answers
207 views

RS-232 and RS-485 software configurability?

I would like to connect a anemometer(RS-485, DB9) to the PC. The PC has a serial port with DB9 connector. I couldn't find the specification of the serial port. Is that RS-232 standard or RS-485? Most ...
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1answer
113 views

Why does it hase a power supply for the rs232 to rs422?

We have a anemometer with RS422/485 communication, and we would like to connect to the PC, but we have only RS232 so I would like to purchase a converter, but some converter has an external power ...
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140 views

Transmitting pulses via RS485

I will have an IR led / photo transistor based reflective sensor, measuring rotation speed of a wheel, producing pulses using a comparator with hysteresis. The pulses will be counted by ...
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545 views

RS485 Cable Lengths and Reflections

In our lab we have setup a RS485 network with short cables and the network is working fine. I know that terminating resistors are required, especially with longer cables lengths due to reflections on ...
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542 views

RS485 how to tell if HXPS-2108F Prolific is working

newbie at electronics (not PC's or software) - my first project is to connect the PC up to a Solar Power Inverter to datalog. Aurora inverter.. great wiki here ...
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Is CAT5 cable good enough for RS-485 vs “true” RS-485 cable

I have a serial comms project coming up. A number of boards with RS-485 interfaces need to communicate. Date rate is 57600bps and cable length will be less than a few hundred feet. Will shielded ...
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403 views

Unused twisted pair termination with RS-485 on 8P8C

For my digital electronics project, I'm making a device which will among other things have RS-485 communication. From what I've seen, the recommended cable type for RS-485 is twisted pair, and one of ...