Point:1. Serial Port and comport are physical interfaces (hardware ). While TTL, RS-232, RS-485 refers to the level standard (electrical signal ). 2. Generally, only Gnd RX Tx is connected to the device. Do not connect to the VCC or + 3.3v power cord to avoid power supply conflicts with the target device. 3. The pl2303 and cp2102 chips are USB-to-TTL serial ports. They use USB to expand the serial ports (TTL level ). 4, maxcompute chip is TTL level and RS232 level of the dedicated two-way conversion chip, you can TTL to RS-232, you can also RS-232 to TTL. 5. the TTL standard is that the low level is 0, and the high level is 1 (+ 5 V ). RS-232 standard is positive electrical flat is 0, negative electrical flat is 1 (+ 15 V level ). 6. RS-485 is similar to RS-232, but negative logic of differential signal is adopted. I will skip it here.
Serial Port and comport:The comport is a serial communication port. This is different from USB's "Universal Serial Bus" and hard disk's "SATA ". We generally see two physical standards.
Type D 9-pin connector, And
4-pin Dupont head. This is common
4-pin serial port, Common on the circuit board, often with DuPont pins on top. There is also the fifth needle, 3.3v power supply end. Because it is reserved on the circuit board, there are many protocols, depending on the specific device. Below is
D-type 9-pin serial port(In general ). It can be seen behind the desktop computer. Remember, there are only two protocols for this interface: RS-232 and RS-485. It will not be a TTL level (unless used in special applications ). 9-pin serial port definition can refer to here: http://wenku.baidu.com/view/5c170c6925c52cc58bd6be6e . HtmlGenerally, we only take the rxd txd And Gnd. It is a small board for USB-to-TTL serial port. You can use USB to expand a serial port. The chip is pl2303hx. Various serial ports are often obfuscated on the Internet, but this can indeed be used to download the program for the STC microcontroller. This is another type, cp2102 chip, also USB to TTL serial port. It is said that it is better than pl2303, but it is not felt in actual use. This small Board has an additional power supply end of + 3.3v to adapt to different target circuits.
The above are all USB to TTL serial port, if the target device is RS-232 serial port (d 9 pin Interface) How to get it? Next, convert a piece of maxcompute. You can also build a simple comparator circuit to realize the function of TTL to RS-232, such. RS-232 to TTL how to get? This requires a bit of attention.
Of course, some people thought of making a finished product. Take a closer look, USB after pl2303 into the TTL serial port, the four holes in the middle can be drawn out, and then converted to the RS-232 level through maxcompute, 9-pin serial port. The following is another example: level conversion still uses maxcompute.
You may buy this: It looks like there is only one cool chip in it.
But remember one point, as long as the D-9 serial port, will not be TTL level, no special instructions on the default is RS-232. So this line, no matter what is constructed inside, is the USB to RS-232 serial line.
I would like to emphasize that a device serial port can be based on the serial line to determine whether it is TTL or RS-232, thus determining the connection mode and whether the need to convert the circuit.
