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Read the meaning of serial port and various level signals
2022-04-23 15:52:00 【ZONG_ XP】
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Students who do embedded development or hardware development , You must hear it often RS232、RS485、TTL And so on , If you are not clear about these concepts , There will be problems in use , This paper introduces the meaning of these concepts ( See if the picture below is dizzy )
1 A serial port
First of all, make it clear , A serial port 、COM Port refers to the form of hardware interface , and TTL、RS-232、RS-485 Refers to the level signal
1.1 UART Interface
Universal asynchronous transceiver (UniversalAsynchronous Receiver/Transmitter),UART It is the logic circuit of serial port transceiver , This part can be made into a chip , It can also be embedded into other chips as a module , Single chip microcomputer 、SOC、PC There's going to be UART modular .
UART Yes 4 individual pin(VCC、GND、RX、TX), It's using TTL level , The low level is 0(0V), The high level is 1(3.3V Or more ).
1.2 COM mouth
COM Port is the serial communication port , Serial port for short , It's very common D type 9 Pin plug , There are only two protocols for this interface :RS-232 and RS-485. Will not be TTL Level . Generally, only RXD、TXD, Plus GND.
1.3 USB mouth
Universal serial bus , And serial port are two concepts . Although it's also serial communication , But because of USB The communication timing and signal level are completely different from serial port , So it has nothing to do with the serial port .USB It's a high-speed communication interface , be used for PC Connect all kinds of peripherals ,U disc 、 Key mouse 、 mobile hard disk drive 、 And of course "USB To serial port " Module .(USB Serial port module , Namely USB Interface UART modular )
2 TTL
TTL level : full duplex ( Logic 1:2.4V ~ 5V, Logic 0:0V ~ 0.5V)
How to connect
Level indication
3 RS232
It is the asynchronous transmission standard interface formulated by the electronics industry association , At the same time corresponding to the level standard and communication protocol ( sequential ), Its level standard :+3V ~ +15V Corresponding 0,-3V ~ -15V Corresponding 1.RS232 The logic level and TTL Not the same, but the agreement is the same .RS-232 Suitable for communication between local devices , The transmission distance generally does not exceed 20m.RS-232 Only one to one communication is allowed .
RS-232 level : full duplex ( Logic 1:-15V ~ -3V, Logic 0:+3V ~ +15V)
Connection diagram
Level indication
4 RS485
RS485 Is a serial interface standard , For long distance transmission, differential transmission is adopted , It's a differential signal , The anti-jamming ability is better than RS232 Much better . The pressure difference between the two lines is -(2~6)V Express 0, The pressure difference between the two lines is +(2~6)V Express 1.RS-485 The transmission distance is tens of meters to thousands of meters .RS-485 The interface on the bus is allowed to connect up to 128 A transceiver .
RS-485: Half duplex 、( Logic 1:+2V ~ +6V, Logic 0:-6V ~ -2V) The level here refers to AB The voltage difference between the two wires .
Connection diagram
Level indication
5 Conversion chip
5.1 USB turn TTL
PL2303、CP2102 The chip is USB turn TTL Serial port chip , use USB To expand the serial port (TTL level ).USB turn TTL The serial port is shown in the figure below :
5.2 TTL And RS-232 Interturn
MAX232 The chip is TTL Level vs RS232 Special bidirectional conversion chip for level , Sure TTL turn RS-232, It's fine too RS-232 turn TTL. Here's the picture :
Reference resources
A serial port 、TTL、232、485 difference _IOT-SYM The blog of -CSDN Blog _232 485 difference
A serial port 、COM mouth 、UART mouth , TTL、RS-232、RS-485 Detailed explanation _ level
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本文为[ZONG_ XP]所创,转载请带上原文链接,感谢
https://yzsam.com/2022/04/202204231547449004.html
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