Questions tagged [rs232]

RS-232 is the electrical standard used on most serial ports. Note that this standard is a +/- 15 volt system and requires a FDMI converter to make it compatible with TTL logic levels.

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Difference between UART and RS-232?

Most of the time RS-232 and UART come together in serial communication theories. Are they both the same? From my readings I concluded UART is a hardware form of the RS-232 protocol. Am I correct?
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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 ...
Sonam's user avatar
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What are the differences between USB and RS232?

Can someone tell me why people use either USB or RS232. They are both serial ports, right? And I understand that USB is much faster (especially USB3.0) but if people wanted too I'm sure they could ...
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24 votes
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Communication between multiple microcontrollers

I'd like to start implementing a system consisting of N microcontrollers (N >= 2 MCUs), but I would like to know the possibilities to let them communicate one with the other. Ideally, (N-1) ...
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What is the meaning of "half bit" in this context?

In RS-232 specification, the stop bits can be 1, 1.5 or 2 stop bits...I wonder how it's possible to have half a bit? Also some ADC math uses 0.5bit precision in the IC specifications/datasheet. Can ...
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17 votes
6 answers
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Max Serial Cable Length?

What is the maximum length of serial cable I can use, to connection work properly? Is length of serial cable in connection with baud rate? I am using about 5 meter cable at speed 38400 bauds and RS232 ...
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Why does RS-232 need a stop bit? [duplicate]

This might be obvious but I don't understand why RS-232 needs a stop bit. I understand that the start bit is necessary to notify the other end about the beginning of a transmission. Let's say we are ...
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RS232 vs USB CDC quality of service / should messages contain a checksum?

Does USB have a quality of service guarantee for data sent between my USB-CDC device and the USB host? I know with traditional RS232 in a noisy situation (e.g. automotive diagnostic port) bad bits ...
Steven T. Snyder's user avatar
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4 answers
27k views

What are TX and RX relative to?

I have been working with a device that uses RS232 communication to a PC. There has been some confusion as they have defined their TX and RX pins relative to the device. In their definitions they use ...
Fr33dan's user avatar
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Why is RS-422 interface interference insensitive?

I am trying to understand differences between RS-232 & RS-485. I just don't grasp what is the core principle behind RS-422 inteference resistance? Is it number of wires (4 instead of 3)? Is it ...
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What is the difference between RS-232 and TTL UART? [duplicate]

I always need to communicate with the TTL UART port on the MCU with a computer. When I talked about that, people always refer the UART port as an RS-232 port. Are they correct? If not, what is the ...
eepty's user avatar
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How does the MAX232 double the voltage?

MAX232 Datasheet Hi, I am currently a student so bear with me please! I'm currently using a powering the MAX232 with 5V DC, and when I measure from VCC to lets say, pin 3, I am getting a voltage ...
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Can we calculate the baud rate of RS232 communication from the TX output signal?

Can we calculate the baud rate or communication speed of RS232 communication from the X output signal? The below image is from an RS232 communication output signal. I took this picture with 0xaa, and ...
chiper's user avatar
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Why is USB cable maximum length is shorter than in RS232?

Why do we need to buffer USB signal if the cable is longer than 5m? Is that because a signal voltage drop? Is that because it drives currents?
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RS232-to-USB Converter [closed]

Anyone have any recommendations on a good rs232-to-usb converter. There are a lot out there and from the looks of it some are hit or miss. Good driver support is a must.
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Why can't I successfully send messages over RS232?

So the past week I have been working on getting UART messages sent from a STM32F407 and reading it on my laptop through a ugreen RS232 to USB cable using termite. I have used STMCube to generate code ...
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What can I do to decrease the latency from these serial ports which are attached to a PC via a Serial to USB adapter?

I think I have accidentally discovered a need in my life for embedded systems. Which is great! And kind of scary. And I need help. Background: I got hired to build a GUI application which takes scans ...
canisrufus's user avatar
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6 answers
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How can I fix an AVRdude not-in-sync error when programming Arduino via USB-to-serial cable?

I'm trying to build this Ambient lighting for PC (original link; updated link). This worked flawlessly on my Arduino Uno. My next step was to make it using "Arduino on a breadboard". So I ...
potato_in_my_ear's user avatar
9 votes
2 answers
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How to use SCPI on HP33120A via RS232?

I have old Hewlet Packard 33120A function generator (it should be the same type as Agilent 33120A) and I would like to control it with MCU (ATMega). The generator has RS232 and use SCPI commands. I ...
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Why are there so many resistors in a typical schematic?

I know that some resistors cause pull-up or pull-down or work as a voltage divider and/or current divider. But sometimes I cannot understand their function in some simple circuits: Take this motor ...
Harry Svensson's user avatar
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3 answers
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What is the maximum acceptable baud rate error for RS-232 serial communication?

What is the maximum clock difference between a transmitter and receiver for error-free asynchronous serial communication?
markrages's user avatar
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How can RS-232 DTR / RTS pins be used for power?

I want to interface to this device where (sec 4.2) states can be powered from the DTR and RTS handshaking lines by having one high and one low Also, Wikipedia states: No method is specified ...
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Selecting communication between microcontrollers at high temperature

I have been assigned to a project to find the best possible communication between several PCB boards which have microcontrollers for a specific function. I need to have all microcontrollers ...
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Crosstalk from RX to TX line on the RS-232 side of MAX3232C

We have a product which is using a MAX3232C for interfacing to a PC. Its RS-232 RX line is tied to the MAX3232's R1IN pin and its TX line to T1OUT: The problem we are having appears to be some kind ...
Claudio's user avatar
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How can a USB-RS232 converter manually assert its TX pin?

I made a custom PICAXE-based PCB that integrates all of the components needed to program the microcontroller. I assumed everything was fine because I could use it to program under Windows just fine. ...
Dave's user avatar
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7 votes
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Why does the MAX3232 have two inputs and two outputs?

I am trying to make a PCB for TTL to RS232 converter. I am using the MAX3232. It looks 10-11, 14-7, 13-8 and 12-9 are the same. I see some diagrams where people only use one of them. For example,in ...
mehmet's user avatar
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Implement serial port on fpga (verilog)

I don't know if this belongs here or stackoverflow. I assume here as although verilog looks like software it's actually describing hardware connections? I have a Spartan-3AN evaluation board and I'm ...
John Burton's user avatar
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856 views

Who decides the timing in the async serial communication based on UART + RS232?

According to here, UART is a hardware device that implement the asynchronous serial communication protocol. And according to here, RS-232 defines the electrical characteristics and timing of signals, ...
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RS-232 Buffer circuit

I wanted to sniff communication between two RS232 devices. This link presents a simple solution but I want to make sure that my 'sniffer' does not load the communication link. To that effect, I was ...
itisravi's user avatar
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7 votes
3 answers
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Opto-coupled RS-232 receive circuit

I am looking into a implementing a low-cost RS-232/422 opto-coupled receive circuit. The aim is surge protection and tolerance to DC offsets. The challenge is that the inputs should be completely ...
ARF's user avatar
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7 votes
2 answers
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Problems with homemade RS232-to-TTL converter board based on TI's MAX232

I've designed an RS232-to-TTL converter board based on TI's MAX232 IC that I plan to use to program a few custom Arduino boards that I have. However, I'm having trouble with the board and I'm hoping ...
Ricardo's user avatar
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7 votes
0 answers
477 views

When exactly was the RS-232 standard issued? [closed]

This year is 50th anniversary of RS-232 standard. Despite its age it is still used nowadays, and I work in company that has to deal with it. So we have a half-serious idea to celebrate the exact day ...
aimozg's user avatar
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6 votes
5 answers
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Can I use 10\$\mu\$F caps in a MAX232?

this is just a quick and dirty question. I don't understand the purpose of the 1 \$\mu\$F caps in the MAX232 circuit. What do they do, exactly? Can they be skipped? Can they be swapped with 10 \$\mu\$...
Rick_2047's user avatar
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6 votes
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How to connect uC to PC using RS232 with minimum number of signals?

The standard 9 pins RS232 connector has 9 pins. Those are: 1 -- DCD -- Data Carrier Detected 2 -- RxD -- Receive Data 3 -- TxD -- Transmit Data 4 -- DTR -- Data Terminal Ready 5 -- GND -- Signal ...
mazurnification's user avatar
6 votes
7 answers
3k views

Best PC interface for simple custom hardware

What interface of your PC do you use in order to connect to simple custom hardware? The most commonly used interface was RS232 some while ago and today is probably USB, but wouldn't it be simpler for ...
Penguin Nurse's user avatar
6 votes
3 answers
1k views

Must RS-232 devices use the same logic level?

I want to interface a microcontroller with the RS-232 COM port of my PC. My PC uses a 75232G IC, which uses +/-12V logic levels as per some multimeter tests. Currently I'm planning to use the ...
StefanoN's user avatar
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2 answers
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What is the difference between RS-232 and RS-232-C?

I know about RS-232. Later, I heard about RS-232-C. Are these two standards the same or not? If not, what are the differences?
shafeeq's user avatar
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MAX3232 overheating/burnt after connecting to PC

I've got a MAX3232 Serial-to-TTL RS232 board which I am currently using in factory assembly lines. I don't have its picture, but here's a similar product: This is the circuit I've managed to figure ...
Sodrohu's user avatar
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4 answers
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Do I have to use a MAX232 chip?

I am trying to interface my ATmega chips to the computer using a serial interface. I have read that this can be done directly by connecting the appropriate pin between the chips and the serial pin. ...
Rick_2047's user avatar
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6 votes
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History question - why are logic levels inverted between TTL and RS232?

I'm just looking for a historical answer as to why TTL and RS232 don't transition logically in the same directions. The signals are the same, but basically level-shifted and inverted. Was there a ...
David Carta's user avatar
6 votes
2 answers
7k views

RS 232 serial sniffing

We have a task in hand to sniff a RS232 protocol in a certain industrial automation setting (we have been asked to do this legally by the manufacturing company itself). We are planning to send a ...
Elsa Adams's user avatar
6 votes
3 answers
6k views

When do we use all pins in RS-232 cable?

I think the minimum for simplex communication are TX so we can transmit and the power supply pins +Vcc and GND. That is all we need. When do we need to use all 9 pins of RS-232? I think that the ...
quantum231's user avatar
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Recommendation of a USB-to-RS-232 chip for an industrial environment

I have bought a device which has an ATmega microcontroller and an FTDI chip which connects to a computer through USB. The FTDI is used only as an RS-232-to-USB adapter. My problem is that this device ...
drzymala's user avatar
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6 votes
2 answers
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Why is RS422a more immune to electrical noise than RS232?

I have read that RS-422a cable uses a 20 mA current loop instead of voltage levels. This makes the systems more immune to electrical noise, so the cable can be up to 3000 feet long. I do not ...
KMC's user avatar
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Do I need MAX232 when using USB-to-Serial cable?

I am willing to build an AVR JTAG debugger (I grabbed from here: http://aquaticus.info/jtag) but the circuit uses COM port and it has MAX232 transceiver. My Laptop does not have COM port, so I need a ...
Siraj Muhammad's user avatar
6 votes
4 answers
1k views

Trying to figure out available resources on MSP430 LaunchPad

I'm just starting to mess with the MSP430 and have some simple apps working fine. However, now I want to use it with an LCD and am trying to determine if I'm short on I/O. For sure, I'll need to use ...
Dave's user avatar
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Is anything besides rx and tx actually used in rs232 nowadays?

Whenever I come across a PIC or even a FPGA project that is communicating over the serial port with a PC; only Rx, Tx and power are connected on the 9 pin connector and the other pins/signals are ...
quantum231's user avatar
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Why MAX232 works without any capacitors?

I was playing today with a very simple setup of pic16f876 and max232 connected to the COM port of a PC running a terminal emulator. I was just testing (the uc simply echoes anything it receives) when ...
Cleric's user avatar
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6 votes
2 answers
964 views

RS-232 switching

I have a modem connected to a server through RS232. The server is constantly sending data to the modem, whether the modem is connected or not. When I try to connect to the modem with another modem ...
Handshaking's user avatar
6 votes
1 answer
920 views

Serial data transfer from Omega DP80 legacy hardware to computer

Can anyone provide me with some guidance on setting up a legacy serial connection on an Omega (brand) thermocouple display? I would like to use the serial data interface (Omega DP80-Ser) to reliably ...
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