# Tag Info

## Hot answers tagged rs232

Accepted

### Difference between UART and RS-232?

No, UART and RS-232 are not the same. UART is responsible for sending and receiving a sequence of bits. At the output of a UART these bits are usually represented by logic level voltages. These bits ...
• 36k

### Difference between UART and RS-232?

UART (or USART) - Universal (Synchronous) Asynchronous Receiver/Transmitter This is, essentially, a serial communications interface. The "universal" part means that it can be configured to support ...
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### What does 232 signify in the RS232 standard?

It signifies nothing; it's part of a sequential list of EIA standards: -
• 384k
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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 ...
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### Why does RS-232 need a stop bit?

The thing to remember is that RS232 is an asynchronous protocol. There is no clock signal associated with it. Figure 1. Receiver sampling points. Source: Sangoma. The start bit is used to trigger ...
• 160k
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### What are TX and RX relative to?

It might be easier to understand, if we quickly review how the RS-232 standard was originally used. Note: All pin numbers below refer to the original 25-pin D connector; the numbering changed on the ...
• 16.7k
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### Can I connect two microcontrollers via RS232 separated by a distance of 3.5 inches? Both are on two separate PCBs

If the distance is really 3.5 inches, it is quite absurd to think that when connecting two UARTS together you must use RS-232 tranceivers. You don't need to use RS232 tranceivers and you don't need ...
• 89.9k

### Difference between UART and RS-232?

The UART functions to convert parallel data from PC bus lines to serial data for transmission via line drivers to RS-232, RS-422, and RS-485 devices. The clock pin of the UART chip is feed by a ...
• 241

### Can we calculate the baud rate of RS232 communication from the TX output signal?

It looks like you have about 2.4 bit times per division, which are 250 µs. That puts each bit time at 104 µs. Inverting that yields 9.6 kBaud. That's one of the standard baud rates, so ...
• 306k
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### Why can't I successfully send messages over RS232?

You have missed a major detail of RS232. Logic levels are as follows: Figure 1. RS232 signal levels. Source: Wikimedia Commons. Logic 1 = -3 to -12 V. Logic 0 = +3 to +12 V. Between -3 and +3 the ...
• 160k
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### Why are there so many resistors in a typical schematic?

All three circuits display examples of pull up, pull down, voltage dividers, and current dividers: R1 and R2 are pull up ...
• 20.1k

### Is Ethernet synchronous or asynchronous serial?

I think you're getting multiple answers, because the real answer is that you can't quite wedge what the various flavors of Ethernet are into the definitions of "synchronous serial" or "...
• 36.3k
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### Why does the MAX3232 have two inputs and two outputs?

Many RS232 peripherals use control signals, e.g. CTS/RTS, in addition to the TX/RX data lines, so they would need another transmitter/receiver. If you plan to make a general purpose RS232-DB9 module, ...
• 1,052
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### How does the MAX232 double the voltage?

It uses one charge pump to double the supply voltage, and the second charge pump to invert it. The idea behind the charge pump doubler is that capacitors are first charged in parallel, then they are ...
• 36k

### DB9 male or female Connector in Board

The original plan when the D-sub connector family was introduced was that equipment would always have female connectors and cables would always have male connectors. The idea was that pins are easily ...
• 165k
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### Why is USB cable maximum length is shorter than in RS232?

Speed of transmission matters because USB is half-duplex: in order to transmit a response, the bus must be turned around and data transmitted in the other direction. So the host sends out data and ...
• 45k
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### Max Serial Cable Length?

Capacitance in the cable begins to affect serial communications, typically many manufacturers/devices set a limit of approximatly 15m or 50ft on cable lengths for anything up to 9600 baud, and about ...
• 4,075

### UART frequency in microcontrollers

1) Why the frequency should be 16 times the baud rate? As Chris has already pointed out in the comments, there is no clock signal, RS-232 UARTs are asynchronous systems. This means we have no idea ...
• 6,792

### Why are there so many resistors in a typical schematic?

In the case of the Zener regulator, the supply is 10 volts, and the Zener will do its best to limit the voltage across itself to 6 volts. If the 40 ohm resistor wasn't there, a very large current ...
• 51.7k

### RS-232 for approx 1600ft

Can someone please suggest on what should be the correct approach to enable communication using RS-232 for such long distance. No, because RS-232 was never designed to work over such distances. A ...
• 12.7k

### History question - why are logic levels inverted between TTL and RS232?

This is partly speculation, but here goes: Originally, asynchronous serial interfaces were current loops. In order to make things like detecting wiring faults easier, the "idle" state was ...
• 165k

### Can I connect two microcontrollers via RS232 separated by a distance of 3.5 inches? Both are on two separate PCBs

No, your microcontrollers will not communicate using RS-232 unless you're using RS-232 levels, which only your second option does. What you mean with (RX, TX, CTS and RTS lines) is that they're ...
• 78.3k

### Can we calculate the baud rate of RS232 communication from the TX output signal?

Your scope shows the timing at $100\:\mu\textrm{s}$. This may either be you setting the cursors, or else the automated use of a measure function on the scope. You don't say. Either way, I agree with ...
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### Is the ATMEGA328P's serial baud rate quantised?

It is a fully digital system. It must operate in discrete steps. This is the formula from the datasheet: UBRR register is 16 bits wide (UBRRL + UBRRH), so it can only lead to 65536 possible baud ...
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### Is Ethernet synchronous or asynchronous serial?

Ethernet has no separate wire for clock signal, so does it make it asynchronous? Not having a separate wire means nothing. Some ethernet data uses Manchester encoding and some use data scrambling. ...
• 384k

### Can I connect two microcontrollers via RS232 separated by a distance of 3.5 inches? Both are on two separate PCBs

One thing not mentioned in the other answers, is that not only you don't need RS232 transceivers at such a short distance and so low speed, but the use of flow control signals is also a waste of MCU ...
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### Why does the MAX3232 have two inputs and two outputs?

It has two inputs and two outputs. What you do with them or not depends on what your application requires. You can make an RS232 adapter with two RS232 ports that both only support TXD/RXD, or you can ...
• 89.9k

### Why is USB cable maximum length is shorter than in RS232?

See this page, https://superuser.com/questions/64744/maximum-length-of-a-usb-cable. Q1: How long of a cable can I use to connect my device? A1: In practice, the USB specification limits the ...
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### What is the difference between RS-232 and RS-232-C?

The RS-232 Standard has gone through several revisions over the years. In the original RS-232, the signal would flip between positive and negative 25 volts. Since that point there have been three ...
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