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40 votes

What does 232 signify in the RS232 standard?

It signifies nothing; it's part of a sequential list of EIA standards: -
Andy aka's user avatar
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30 votes
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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 ...
slebetman's user avatar
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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. ...
Tom Carpenter's user avatar
22 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-...
Olin Lathrop's user avatar
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 ...
metacollin's user avatar
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18 votes

Do FTDI serial port chips use a soft UART, or a hardware UART?

The cable you are talking about uses an FT232RQ chip. Based on the cable schematics the chip is set to RS-485 mode, where a separate TXEN line is used to enable the RS-485 PHY transmit mode, instead ...
Justme's user avatar
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15 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 ...
Michael Karas's user avatar
14 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 ...
Olin Lathrop's user avatar
13 votes
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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 ...
Michael Karas's user avatar
12 votes
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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 ...
Transistor's user avatar
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12 votes

What protocol is this waveform?

You have done excellent reverse-engineering. Everything does point out to RS-485 physical interface with UART protocol and the bit rate is likely just standard 38400 bps based on the measurements of 3 ...
Justme's user avatar
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12 votes

Standard pinouts for RS485_interface

Connectors are not part of RS-485 standard. As the old joke has it, standards are so good everyone should have their own: Here are several conflicting specifications for half-duplex RS-485 on D-shell ...
jonathanjo's user avatar
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11 votes
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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 ...
John Burger's user avatar
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11 votes

Do FTDI serial port chips use a soft UART, or a hardware UART?

Your question seems muddled due to mixed up terminology. Here are what the words actually mean: Hardware UART: There is a dedicated peripheral in a controller that contains dedicated register and ...
DKNguyen's user avatar
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10 votes
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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 ...
Andy aka's user avatar
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10 votes
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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 ...
Timmy Brolin's user avatar
10 votes
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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 ...
Andy aka's user avatar
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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 ...
Jeroen3's user avatar
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9 votes
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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. ...
Maple's user avatar
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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 ...
CL.'s user avatar
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8 votes
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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 ...
Andy aka's user avatar
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8 votes

What protocol is this waveform?

Since the FCC authorisation code is marked on the device, you can look it up on the FCC database. If you enter the first 3 characters (SH6) as the grantee code, you get a list of devices from that ...
jayben's user avatar
  • 1,367
8 votes

RS485 star topology

As others have said, it all comes down to how far and how fast, and how long the stubs are. but the simplest solution just uses more wire. Have you considered wiring which is Electrically a Bus and ...
jonathanjo's user avatar
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7 votes
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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 ...
Olin Lathrop's user avatar
7 votes
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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 ...
Andy aka's user avatar
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7 votes
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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 ...
DiBosco's user avatar
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7 votes
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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 ...
DKNguyen's user avatar
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7 votes
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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 ...
Andy aka's user avatar
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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 ...
Davide Andrea's user avatar

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