Uart refers to the TTL level serial port; RS232 refers to the RS232 level serial port. The TTL level serial port is the input and output end of the serial port of the general chip, and the chip that can not be connected can complete the peripheral function. Let's take a look at what the definition of TTL level and RS232 is, and then see if their serial port is different.
The reason why TTL level signals are widely used is that we usually use binary to represent data. Furthermore, it is stipulated that +5V is equivalent to logic "1" and 0V is equivalent to logic "0". Such data communication and level regulation methods are referred to as TTL (transistor-transistor logic level) signal systems. This is the standard technique for communication between various parts of a device controlled by a computer processor.
The TTL level signal is ideal for data transmission inside a computer controlled by a computer processor. First, the data transmission inside the device controlled by the computer processor is not required for the power supply and the heat loss is low, and the TTL level signal is directly It is connected to the integrated circuit without the need for expensive line drivers and receiver circuits. Furthermore, the data transfer inside the device controlled by the computer processor is performed at a high speed, and the operation of the TTL interface can meet this requirement. In most cases, TTL communication uses parallel data transmission, while parallel data transmission is not suitable for distances over 10 feet.
This is due to both reliability and cost. Because of the problems of bias and asymmetry in the parallel interface, these problems have an impact on reliability. In digital circuits, the level used by the circuit consisting of TTL electronic components. The level is a voltage range, which specifies the output high level "2.4V" and the output low level "0.4V. At room temperature, the general output level is 3.5V and the output low level is 0.2V. Minimum input high level and low level: input high level ==2.0V, input low level "=0.8V, noise margin is 0.4V.
RS232 is one of the communication interfaces on personal computers, and is an asynchronous transmission standard interface developed by Electronic Industries Association (EIA). Usually the RS-232 interface appears in the form of 9 pins (DB-9) or 25 pins (DB-25). Generally, there are two sets of RS-232 interfaces on the personal computer, which are called COM1 and COM2. . Take a look at the serial port difference.
The difference between Uart serial port and RS232 serial portThe TTL level is 3.3V, while RS232 is a negative logic level, which defines +5~+12V as low level and -12~-5V as high level.
The RXD and TXD of the Uart serial port are generally directly connected to the pins of the processor chip, and the RXD and TXD of the RS232 serial port generally need to be level-converted (usually level-shifted by a chip such as Max232) to be connected to the processor chip. On the pin, otherwise such a high voltage is likely to burn the chip.
The serial port of the computer we usually use is RS232. When we are working on the circuit, we should pay attention to whether the serial port of the peripheral is Uart type or RS232 type. If it does not match, we should find a conversion line (usually this conversion line) There is a chip similar to Max232 for level conversion work), you can not blindly connect the two serial ports.
In addition, add another point. When you make the serial line yourself, generally follow the following rules:
PC-compatible peripherals (such as a development board)
GND ------- GND
RXD ------- TXD
TXD ------- RXD
CTS ------- RTS
RTS ------- CTS
Usually it is the same as the above crossover, but if the RXD of the serial port on the development board is connected to the TXD of the CPU on the board, the other is similar, that is, it has been crossed once, then when we are making the serial line It is not necessary to follow the above correspondence, but RXD corresponds to RXD, TXD corresponds to TXD, and the others are the same.
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