RS232 serial port introduction and pin function definition, serial port definition, DB9, RS232

 

The RS232 interface is a standard for serial communication jointly developed by the American Association of Electronic Industry (EIA) and bell system, modulation regulator manufacturers and computer terminal manufacturers in 1970.

Its full name is "Technical Standard for Serial Binary data exchange interfaces between data terminal devices (DTE) and data communication devices (DCE)", which requires a 25-pin db25 connector, specify the signal content of each pin of the connector and the signal levels. Generally, only 2 (rxd), 3 (txd), and 7 (Gnd) pins are used in the db25 serial port. With the continuous improvement of the device, db25 pins are rarely seen, instead of DB9, DB9 uses three pins: 2 (rxd), 3 (txd), and 5 (Gnd. Therefore, the RS232 interface is called DB9.

The early appearance of RS232 interface standards inevitably led to the following shortcomings:

(1) The signal level value of the interface is high, which is easy to damage the chip of the interface circuit. Because it is not compatible with the TTL level, the level conversion circuit must be used to connect to the TTL circuit.

-15v ~ 0 V = binary 1, 0 ~ + 15 V = binary 0

(2) low transmission rate. During asynchronous transmission, the baud rate is 20 kbps;
(3) The interface uses a signal line and a signal return line to form a co-location transmission mode. This co-location transmission is prone to common-mode interference, so the anti-noise capability is weak.
(4) The transmission distance is limited. The maximum transmission distance is 50 feet. In fact, it can only be used about 50 meters.

 

 

 

 

Pin definition symbol (9-core)

1. Carrier Detection DCD
2 receive data rxd
3 send data txd
4. Prepare DTR for the data terminal
5-signal SG
6. Prepare data for the DSR
7. Send an RTS request
8. Clear sending cts
9. When the ring is set to RI