40
votes
What does 232 signify in the RS232 standard?
It signifies nothing; it's part of a sequential list of EIA standards: -
- 390k
30
votes
Accepted
What does 232 signify in the RS232 standard?
It's the document serial number of the standard. Same reason why the HTTP protocol is also known as RFC2616 and the Javascript programming language is also known as ECMA262.
The numbers themselves ...
- 1,650
23
votes
How to find the UART line is free for send data
Welcome to the biggest challenge with half-duplex communications systems.
RS-485 is not a protocol, it's a standard which defines the electrical properties for a half-duplex(*) differential link. ...
- 57.7k
19
votes
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Can I send PWM through 1 meter cable?
The PWM frequency is not so important, what matters is the rise times of the switch controlling the PWM. Assuming it is some sort of MOSFET, one can assume very fast rise times of 100ns to 10ns or ...
- 26.4k
17
votes
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Significant differences between CAN and RS485 regarding the physical layer
When comparing the physical layer only, CAN and RS-485 are similar in that they both use differential signaling. This gives them both good common mode noise immunity.
The main difference is that RS-...
- 307k
16
votes
Accepted
Correctly using RE and DE with RS485
You don't need any pull-up or pull-down resistors if you're driving those pins with normal output pins on your micro.
DE is the 'Driver Enable' pin and must be pulled high while you're transmitting ...
- 13.4k
13
votes
RS485 network ground pin - when to connect?
It is a myth that you can make RS485 interfaces work without the Common (C) ground wire connected up between the various devices on the bus. The receiver is only capable of measuring the relative ...
- 55.4k
13
votes
Accepted
Does a MAX485 need decoupling capacitors?
Yes. All almost ICs need decoupling capacitors. Devices such as these '485 drivers especially need them due to the current surges the device experiences when switching the signal states due to the low ...
- 55.4k
12
votes
RS485 network ground pin - when to connect?
You are right in that a pure receiver could just measure the difference between the two signal lines. However, any means to do that will have some common mode range that the individual signals must ...
- 307k
11
votes
Accepted
RS485 terminating resistor power rating
I suspect the answer is in bold in the first line of your question. The resistor is between the data lines but the differential voltage is only a few volts - the common mode voltage can be anything ...
- 161k
10
votes
Accepted
Why common-mode choke on differential-signal serial lines?
Wouldn't the common-mode noise simply be cancelled in the receiver?
A lot of noise would be heavily cancelled in a differential receiver but, high frequency stuff can cause problems and, of course a ...
- 390k
9
votes
Accepted
How is this RS485 Module Working?
More than likely it switches into transmit mode when TXD becomes active and a diode and capacitor "latch" that first transmit edge and hold that voltage "active" for longer than at least one byte.
I ...
- 390k
9
votes
RS 485 ground signal and chassis
Looks like a common mode voltage problem to me. Although differential signalling, it still needs a common GND.
(source)
Replace your 1nf 500v capacitor with a jumper. Or wire signal ground to all ...
- 21k
9
votes
Accepted
Could Cat5e be used for RS485
Short answer: yes.
That should work just fine.
It is quite common to use CAT5 for RS485.
More detailed:
RS485 requires a common ground reference for all devices. Yes, you can use spare pairs in the ...
- 643
9
votes
The origin of the "cable length - data rate" graph in the RS-485
At the right, the data rate is limited by the capabilities of the transmitter and the receiver.
At the top, the cable length is limited by the (standardized) drive strength of the transmitter.
At the ...
- 14.9k
8
votes
Accepted
Connect RS422 interface with Arduino Uno
To answer this I need to explain a few things. (TL;DR? See Consequences below.)
Voltages
There are a number of different serial hardware solutions, to solve different problems.
TTL:
The Arduino's ...
- 1,423
8
votes
Accepted
Is it OK to use RS485 with separate wires for each device?
Both of these will work providing you apply the modifications in red: -
Both distant ends of the cable need a suitable termination resistor to protect data reflections causing corruption of the data ...
- 390k
7
votes
Accepted
RS-485: Error detection/correction mechanism
RS-485 and RS-232 a electrical-only standards. The same data encoding scheme is usually used on both. The difference is that RS-232 uses a single wire for the signal with levels below -5 V and above ...
- 307k
7
votes
Accepted
Do I have to use a MAX485 chip in front of an ATXMega microcontroller?
Wiki says: -
DMX512 employs EIA-485 differential signaling at its physical layer,
in conjunction with a variable-size, packet-based communication
protocol. It is unidirectional.
So you need to ...
- 390k
7
votes
Accepted
RS485 Common Ground: Common Voltage or Common Wire or Both?
You have basically two questions in one.
1. Common ground
With 1000m between the nodes it is practically unavoidable to have ground potential out of transceiver's common mode range at some point. ...
- 10.8k
7
votes
Why common-mode choke on differential-signal serial lines?
The differential receiver has a limited range of common mode rejection, on the order of volts. It cannot remove common-mode noise peaks whose voltage exceeds that level. The common mode choke ...
- 4,758
6
votes
Accepted
What is the relationship between DMX and RS485? Are there any breaks in the protocol in relation to one another?
Basically RS485 is a description of a bidirectional communications hardware interface in which devices speak a known, but adjustable baudrate and byte/character encoding is very similar to RS232. How ...
- 18.1k
6
votes
Accepted
Transit between RS485 and CAN
If I had to design a product that needed to be able to connect to either CAN or RS-485, I'd probably start by considering separate connectors or separate pins on the same connector for the two busses. ...
- 307k
6
votes
How is this RS485 Module Working?
I reverse engineered the exact board pictured in the asker's post. The resistor and capacitor values are not what are there on the board - I selected them for my own circuit. However the schematics is ...
- 73
6
votes
Accepted
Current consumption for RS485 transceivers?
Did you estimate the proportion of time your system will actually be transmitting data? In most applications, this is very small, proabably less than 1%. Most of the time, transceivers are just idle. ...
- 15.6k
6
votes
Accepted
RS485 without flow control
RS485 is a multidrop bus, which means that a number of nodes are connected to the same bus and, in this case, they all have the potential to "talk" at the same time. For a device to take ...
- 1,334
6
votes
Accepted
LM317 power regulator ajust is affected by MAX485 chip
According to MAX485 datasheet, for DIP/SOP packages the ground goes to Pin5, and +5Vcc goes to Pin8. You seem to have the chip powered upside-down.
- 37.5k
6
votes
Accepted
RS-485 network with multiple masters
Is there any risk of damaging chips if one is sending a high bit (0v because it's UART) when others are staying high (idle or low bit)?
My understanding is that multi-master RS-485 (at least one ...
- 48.3k
6
votes
Accepted
RS422, RS485 Termination Resistors
When you send a high speed signal down a cable, the current that initially flows is dictated by the voltage applied AND the characteristic impedance of the cable. For the types of cable recommended ...
- 390k
Only top scored, non community-wiki answers of a minimum length are eligible