Questions tagged [rs485]
EIA RS-485 is a serial communication standard using differential signaling.
579
questions
37
votes
3
answers
9k
views
What does 232 signify in the RS232 standard?
"RS" in communication standards RS232 and RS485 stands for "Recommended Standard". But what information does "232" or "422" or "485" convey in the name? What naming convention is used for numbers ...
- 441
26
votes
8
answers
93k
views
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 ...
- 485
19
votes
5
answers
10k
views
RS485 network ground pin - when to connect?
As many know, one can implement a simple node to node rs485 communication by using only two wires, A and B. Well, the standard specify to connect the ground of the two node together.
from Wikipedia:
...
- 1,430
14
votes
3
answers
24k
views
At what cable lengths are termination resistors required for RS-485 networks?
I've noticed my experiments in the lab with RS-485 work fine with fairly short cables, but termination resistors are needed for true installations. Is their presence or absence a function of the ...
- 1,637
14
votes
2
answers
20k
views
Significant differences between CAN and RS485 regarding the physical layer
In comparing the physical layer of CAN and RS485, I am trying to find the advantages of either one over the other. I found out that they are quite similar. Both are good in terms of common mode ...
- 686
10
votes
3
answers
2k
views
The origin of the "cable length - data rate" graph in the RS-485
In several RS-485 application notes one can find a graph that describes the relationship between data rate and cable length, like this one:
But not a single document describes how to calculate it on ...
- 580
10
votes
3
answers
16k
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 RS-...
- 1,805
10
votes
1
answer
9k
views
RS-485 shield and ground wiring practice
After some reading I was convinced that I have three options:
The best: connect A and B lines to a twisted pair, signal ground (SG) line to therd wire in the cable (or to a second twisted pair) and ...
- 2,932
9
votes
8
answers
3k
views
How to find the UART line is free for send data
I have several boards that communicate together with Rs485. They have ATMega series microcontrollers such as atmega168p or ...
- 183
9
votes
2
answers
1k
views
What protocol is this waveform?
I'm trying to reverse engineer a communication line between two components. However for debugging I'm connecting to only one of them, powering it up and looking at the signal. I have no experience ...
- 191
9
votes
3
answers
25k
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 ...
- 565
9
votes
2
answers
9k
views
RS485 terminating resistor power rating
As far as i know rs485 specifies a bus common mode
voltage of: -7V to +12V
the terminating resistor is 120ohm , using VxV/R , yields high power rating to the resistor , certainly more than 1w . (...
- 3,159
9
votes
3
answers
3k
views
RS485 termination: AC + failsafe + parallel + bidirectional
Knowing that I need to refine my RS485 circuitry, I've been reading. I have a series of specific questions and I hope that you'll indulge me as I describe how I attempted to follow through an ...
- 3,067
9
votes
4
answers
791
views
RS485 minimum node spacing - 3 x RS485 device on PCB
I would like to ask something about RS485 minimum node spacing which is described in (Page 5)
TI Design guide
I would like to create device which consists from 3 existing RS485 devices. My plan was ...
- 91
8
votes
4
answers
3k
views
Can I send PWM through 1 meter cable?
I am working on a project where I need to drive two LEDs on a PCB (= PCB_LED) which is 1 meter away from another PCB (= PCB_MCU).
The PCB_MCU includes a microcontroller with two LED drivers. Each LED ...
- 509
8
votes
4
answers
2k
views
Why common-mode choke on differential-signal serial lines?
I have 2 questions:
Why using a common-mode choke on serial communication lines (like CAN, RS485) if the signal is differential? Wouldn't the common-mode noise simply be cancelled in the receiver?
I ...
- 83
8
votes
6
answers
8k
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 ...
- 1,637
8
votes
2
answers
898
views
RS485 Common Ground: Common Voltage or Common Wire or Both?
RS485 connection needs a common ground, but I am very fuzzy about how that works over longer distances and more complex systems.
When the transmitter and receiver are about 1000m apart, there will be ...
- 552
8
votes
2
answers
2k
views
Sensor Polling via USB-RS485 Serial Interface stuck at 16ms, even though it should be faster
I have a setup, connecting a Razor IMU sensor board, with a RS-485 Breakout board, to a USB-RS485 Serial Interface via USB-cable into my laptop. I run a software on the laptop (Max/MSP) that sends out ...
- 457
8
votes
2
answers
797
views
Effect of "wrong" driver with slightly long RS-485 stubs
I have a planned 250 kbit/sec, single-pair, 36-metre RS-485 installation where it is advantageous for wiring purposes if the stub lengths can be a little longer than optimal. There is a single almost-...
- 10.6k
8
votes
3
answers
6k
views
Do I need biasing resistors on the +/- lines for RS485?
I know I should have a terminating resistor on RS 485.
Do I need biasing resistors on the +/- lines of an RS485 differential signal?
- 821
8
votes
1
answer
3k
views
Effect of splices on 120 Ω twisted pair cable impedance a.k.a correct way to attach stubs to the bus?
I am currently in the process of designing a wiring loom for a race car control system which must also connect a number of devices via a CAN bus.
This is my first encounter with CAN bus (J1939-15) ...
- 83
7
votes
2
answers
13k
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?
- 273
6
votes
7
answers
2k
views
Should I consider using RS-485 for my next project
I am planning on an automation project that will be using several different sensors including but not limited to: Temperature, Barometric Pressure, Air flow, Humidity, etc.
As I was talking with ...
- 1,933
6
votes
3
answers
5k
views
Could Cat5e be used for RS485 [duplicate]
I'm working on a project that will be using RS485 to communicate between a bunch of modules and a master controller. Low baud rate, 9600, but a decent distance, like a couple of hundred feet. I'm ...
- 163
6
votes
7
answers
1k
views
How does the current of RS485 signals return from the receiver to the sender?
I am planning a system consisting of 1 master device which is connected to 19 slave devices using RS485 transceivers. Also, all devices are powered by 1 PSU. A simplified schematic is shown below.
As ...
- 285
6
votes
3
answers
2k
views
RS 485 ground signal and chassis
I have a shielded twisted pair running from one device polling several devices in an RS 485 loop. The conditions:
The devices are in parallel as they should be.
The termination resistors are in ...
- 61
6
votes
2
answers
5k
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
...
- 163
6
votes
2
answers
917
views
Transmitting VCC and GND signals for use with RS-485
The specific question I want to ask is whether I can transmit VCC(5VDC) and GND power signals for powering the destination circuit (in an RS-485 arrangement) or not.
The power lines will be grouped ...
6
votes
1
answer
5k
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 ...
- 63
6
votes
1
answer
2k
views
RS-485 network with multiple masters
I'm building a project with multiple RS-485 senders ("masters") and one receiver:
simulate this circuit – Schematic created using CircuitLab
I'm using one MAX485 as receiver connected to a ...
6
votes
1
answer
3k
views
Blowing out MAX485 transceiver
[Edit: revised my complete post]
I have a problem with a project I'm currently working on, and I would really appreciate some help.
I created 10pcs of 100W RGB LED modules that are communicating via ...
- 1,220
6
votes
2
answers
4k
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 ...
- 1,336
6
votes
2
answers
7k
views
RS-485 isolation required?
I would like to confirm my understanding.
Suppose I 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 same ...
- 1,805
6
votes
1
answer
775
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.
...
- 1,285
5
votes
4
answers
5k
views
RS232 and RS485 over same pins
I have 2 pins and primary function should be A/B RS485, but is possible that I also put RS232 (Rx/Tx) chip on same bus and then control which one I want to use from microcontroller.
I was thinking ...
- 211
5
votes
3
answers
4k
views
MAX485 half duplex Atmega communication problem
I want two atmega32s to communicate over a range of 1000ft, so I decided to use a serial wire for it. I know rs232 is not a good way to communicate over this large range, so I decided to use RS485 ...
- 3,887
5
votes
3
answers
2k
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 ...
5
votes
2
answers
7k
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 ...
- 121
5
votes
2
answers
663
views
Purpose of this oscillator (74HCT14-based) on RS-232 to RS-485 converter?
I am reverse engineering an RS-232 to RS-485 converter to understand how it works. I have attached the schematic that I reverse-engineered from the PCB (apologies for the hand-drawn schematic). I've ...
- 177
5
votes
5
answers
2k
views
RS-485 Stub Connection Best Practices
I have a system with an RS-485 bus master and up to 12 slaves. The master and slaves are located in different assemblies and are connected with an RS-485 bus that is inside a cable harness. The cable ...
- 53
5
votes
2
answers
2k
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 ...
- 457
5
votes
2
answers
716
views
ESD protection on an isolated circuit
I'm currently working on an RS485 DMX circuit and am thinking about proper protective measures.
I've oriented myself on this question. I understand that galvanic isolation does not equal ESD ...
- 173
4
votes
5
answers
2k
views
Do FTDI serial port chips use a soft UART, or a hardware UART?
I'm considering using an FTDI cable for RS-485, and I'm wondering who controls the driver enable and how. Is it in a hardware UART, a soft UART, or by the PC the USB is plugged into (very unlikely).
I'...
- 187
4
votes
3
answers
1k
views
Is it OK to use RS485 with separate wires for each device?
I know common use of RS485 is top wiring diagram. But in my project we need to use RS485 for extend range and reliability connection but connection will be bottom wiring diagram.
Can I use a single ...
- 51
4
votes
1
answer
1k
views
Does a MAX485 need decoupling capacitors?
I am designing a small device with two MAX485 chips.
Do they need the decoupling capacitors on the 5V power?
- 2,438
4
votes
2
answers
9k
views
RS485 without flow control
Is it possible to send/recieve on RS485 without flow control. I am working on stm32f4 platform with a MAX3160 multiprotocol transceiver(supports RS232 and RS485). The UART lines form STM32F4 are ...
- 51
4
votes
4
answers
993
views
RS-485 over many 1000s ft, ground wire and termination always needed?
I've only ever used RS-485 over short connections before. I may have a project coming up where the cables will run several 1000 ft. My questions are:
Is the gnd wire needed?
Should the shield in ...
- 1,637
4
votes
1
answer
5k
views
Hijack/observe RS485 communication data by wire tapping?
I have some Computer -> LED Matrix Screens system like this diagram:
...
- 415
4
votes
4
answers
703
views
Does anyone have any sample code or suggestions to help me to interface my 100 pin uc3a1512to a device via RS-485?
I am attempting to connect and control a device which only accepts RS-485 input. I wish to communicate to this device via my existing UC3A1512. Does anyone have any existing source code or examples ...
- 716