Rs-232 is one of the mainstream serial communication interfaces. It is one of the communication interfaces on personal computers. It is an asynchronous transmission standard interface developed by Electronic Industries Association (EIA). Usually the rs-232 interface is 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. .
Since the rs232 interface standard appears earlier, it is inevitable that there are deficiencies, mainly the following four points:
(1) The signal level of the interface is high, which is easy to damage the chip of the interface circuit. The voltage of any signal line of the rs232 interface is in a negative logic relationship. That is: the logic "1" is -3 - -15V; the logic is "0": +3 - +15V, and the noise margin is 2V. That is, the receiver is required to recognize a signal higher than +3V as a logic "0", a signal lower than -3V as a logic "1", a TTL level of 5V as a logic positive, and 0 as a logic negative. Incompatible with the TTL level, a level shifting circuit is required to connect to the TTL circuit.
(2) The transmission rate is low. In asynchronous transmission, the bit rate is 20Kbps; therefore, in the 51CPLD development board, the integrated program baud rate can only be 19200, which is also the reason.
(3) The interface uses a signal line and a signal return line to form a common ground transmission form. This common ground transmission is prone to common mode interference, so the noise immunity is weak.
(4) The transmission distance is limited. The maximum transmission distance is 50 feet. In fact, it can only be used at about 15 meters.
Rs232 serial port wiring diagram
At present, the more commonly used serial port has 9-pin serial port (DB9) and 25-pin serial port (DB25). When the communication distance is relatively close ("12m"), the cable can be directly connected to the standard rs232 port (rs422, rs485 is far). Far, an additional modem (MODEM) is required. The simplest and most commonly used method is the three-wire connection method, that is, the ground, the receiving data and the transmitting data are connected by three legs. This paper only refers to the most basic connection method and is directly connected by rs232.
Rs232 serial communication wiring method (three-wire system) First, the serial port transmission data can be realized as long as there is a receiving data pin and a transmitting pin: the receiving pin and the transmitting pin of the same serial port are directly connected by a line, two serial ports are connected or one serial port and multiple Serial port connection
1. The receiving pin and the sending pin of the same serial port are directly connected by wires to the 9-pin serial port and the 25-pin serial port, which are directly connected to 2 and 3;
2, two different serial ports (whether the two serial ports of the same computer or the serial ports of different computers)
The above table is for the standard serial port of the microcomputer. There are also many non-standard devices, such as receiving GPS data or electronic compass data, just remember one principle: receive data pins (or lines) and send data pins (or lines). Connected, they cross each other, and the signal grounds correspond to each other.
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