FOCUSES ON PLASTIC INJECTION AND MOLD DESIGN.
DONGGUAN LONGKE ELECTRONIC TECHNOLOGY CO., LTD.
Focus on R & D, production and marketing of precision connectors, electronic connecting lines, metal stamping, mold design
Enterprise mailbox
sales@longke-china.com
NEWS
FOCUSED ON CONNECTOR
主页 > Home > News > Knowledge Encyclopedia >
Knowledge Encyclopedia
A summary and overview of serial data line
- Release date：19-10-23 10:14
- Clicks：116
RS232
It is one of the communication interfaces on personal computer. It is an asynchronous transmission standard interface developed by the Electronic Industry Association (EIA). Usually RS-232 interface appears as 9-pin (DB-9) or 25 pin (db-25). (Electronic Industries Association
The data transmission rate specified in RS-232-C standard is 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud per second.
RS-232-C standard stipulates that the driver is allowed to have a capacitance load of 2500pf, and the communication distance will be limited by this capacitance. For example, when a 150pF / M communication cable is used, the maximum communication distance is 15m; if the capacitance per meter of cable is reduced, the communication distance can be increased. Another reason for the short transmission distance is that RS-232 is a single ended signal transmission, which has common ground noise and can not suppress common mode interference, so it is generally used for communication within 20 m.
The above provisions explain the definition of logic level in rs-323c standard. For data (information code): the level of logic "1" (signal transmission) is lower than - 3V, the level of logic "0" (empty number) is higher than + 3V; for control signal, the level of on (signal effective) is higher than + 3V, the level of off (signal invalid) is lower than - 3V, that is, when the absolute value of transmission level is higher than 3V, the circuit can effectively check out the voltage between - 3 and + 3V. Meaningless. The voltage lower than - 15V or higher than + 15V is also considered meaningless. Therefore, in actual operation, the level should be kept between ± (3-15) v.
Because RS232 interface standard appeared earlier, there are inevitably shortcomings, mainly as follows:
(1) the signal level 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, it needs to use the level conversion circuit to connect with the TTL circuit.
(2) the transmission rate is relatively low. In asynchronous transmission, the baud rate is 20kbps; therefore, in the "Southern old tree 51cpld development board, the baud rate of integrated program 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, which is easy to generate common mode interference, so the anti-noise interference is weak.
(4) the transmission distance is limited. The standard value of the maximum transmission distance is 50 feet. In fact, it can only be used for about 50 meters.
RS485
RS485 adopts differential signal negative logic, + 2V - + 6V means "0", and - 6V - - 2V means "1". RS485 has two-wire system and four wire system. The four wire system can only realize point-to-point communication, which is rarely used now. Now, the two-wire system is mostly used. The bus topology structure can be connected with up to 32 nodes on the same bus. In the RS485 communication network, the master-slave communication mode is generally adopted, that is, one host with multiple slaves. In many cases, when connecting RS-485 communication link, a pair of twisted pair is simply used to connect the "a" and "B" ends of each interface. However, the connection of signal ground is ignored. This connection method can work normally in many occasions, but it has a great hidden danger. There are two reasons: (1) common mode interference problem: RS-485 interface adopts differential mode to transmit signal, and does not need to detect signal relative to a certain reference point. The system only needs to detect the potential difference between two lines. Theoretically, the longest transmission distance of RS485 can reach 1200 meters.
1. Electrical characteristics of RS-485: Logic "1" is represented by + (2-6) V voltage difference between two lines; logic "0" is represented by - (2-6) V voltage difference between two lines. The interface signal level is lower than RS-232-C, so it is not easy to damage the chip of the interface circuit, and the level is compatible with TTL level, so it is convenient to connect with TTL circuit.
2. The maximum data transmission rate of RS-485 is 10Mbps
3. RS-485 interface is a combination of balanced driver and differential receiver, which has better anti common mode interference ability, that is, good anti noise interference.
4. The maximum communication distance of RS-485 is about 1219m, and the maximum transmission rate is 10MB / s. The transmission rate is inversely proportional to the transmission distance. Under the transmission rate of 100kb / s, the maximum communication distance can be achieved. If a longer transmission distance is needed, a 485 repeater needs to be added. Generally, the RS-485 Bus supports 32 nodes at most. If a special 485 chip is used, it can reach 128 or 256 nodes, and the maximum can support 400 nodes.
Because RS-485 interface has good noise immunity, long transmission distance and multi station capability, it becomes the preferred serial interface. Because the half duplex network composed of RS485 interface generally only needs two wires, so RS485 interface adopts shielded twisted pair transmission. The RS485 interface connector adopts the 9-core plug base of DB-9, the interface with the intelligent terminal RS485 adopts DB-9 (hole), and the keyboard interface RS485 connected with the keyboard adopts DB-9 (PIN).
RS422
RS-422 is differential mode transmission, with strong anti-interference ability. It can transmit 1200 meters, and RS232 can transmit up to 15 meters. The principle of RS422 bus is basically the same as that of RS485 and RS422, both of which are sent and received in differential mode, without digital ground wire. Differential operation is the fundamental reason for the long transmission distance under the same speed condition, which is the fundamental difference between RS232 and RS232, because RS232 is a single end input and output, at least three lines (asynchronous transmission) of digital ground wire, transmission line and receiving line are required for duplex operation, and other control lines can be added to complete the synchronization and other functions.
RS422 can work in full duplex mode without affecting each other through two pairs of twisted pairs, while RS485 can only work in half duplex mode, and can not work in both mode, but it only needs one pair of twisted pairs.
RS422 and RS485 can transmit 1142 meters at 19 kpbs. A new transceiver line can be used to connect devices.
One thousand three hundred and ninety-four
IEEE 1394, alias FireWire
It is one of the communication interfaces on personal computer. It is an asynchronous transmission standard interface developed by the Electronic Industry Association (EIA). Usually RS-232 interface appears as 9-pin (DB-9) or 25 pin (db-25). (Electronic Industries Association
The data transmission rate specified in RS-232-C standard is 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud per second.
RS-232-C standard stipulates that the driver is allowed to have a capacitance load of 2500pf, and the communication distance will be limited by this capacitance. For example, when a 150pF / M communication cable is used, the maximum communication distance is 15m; if the capacitance per meter of cable is reduced, the communication distance can be increased. Another reason for the short transmission distance is that RS-232 is a single ended signal transmission, which has common ground noise and can not suppress common mode interference, so it is generally used for communication within 20 m.
The above provisions explain the definition of logic level in rs-323c standard. For data (information code): the level of logic "1" (signal transmission) is lower than - 3V, the level of logic "0" (empty number) is higher than + 3V; for control signal, the level of on (signal effective) is higher than + 3V, the level of off (signal invalid) is lower than - 3V, that is, when the absolute value of transmission level is higher than 3V, the circuit can effectively check out the voltage between - 3 and + 3V. Meaningless. The voltage lower than - 15V or higher than + 15V is also considered meaningless. Therefore, in actual operation, the level should be kept between ± (3-15) v.
Because RS232 interface standard appeared earlier, there are inevitably shortcomings, mainly as follows:
(1) the signal level 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, it needs to use the level conversion circuit to connect with the TTL circuit.
(2) the transmission rate is relatively low. In asynchronous transmission, the baud rate is 20kbps; therefore, in the "Southern old tree 51cpld development board, the baud rate of integrated program 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, which is easy to generate common mode interference, so the anti-noise interference is weak.
(4) the transmission distance is limited. The standard value of the maximum transmission distance is 50 feet. In fact, it can only be used for about 50 meters.
RS485
RS485 adopts differential signal negative logic, + 2V - + 6V means "0", and - 6V - - 2V means "1". RS485 has two-wire system and four wire system. The four wire system can only realize point-to-point communication, which is rarely used now. Now, the two-wire system is mostly used. The bus topology structure can be connected with up to 32 nodes on the same bus. In the RS485 communication network, the master-slave communication mode is generally adopted, that is, one host with multiple slaves. In many cases, when connecting RS-485 communication link, a pair of twisted pair is simply used to connect the "a" and "B" ends of each interface. However, the connection of signal ground is ignored. This connection method can work normally in many occasions, but it has a great hidden danger. There are two reasons: (1) common mode interference problem: RS-485 interface adopts differential mode to transmit signal, and does not need to detect signal relative to a certain reference point. The system only needs to detect the potential difference between two lines. Theoretically, the longest transmission distance of RS485 can reach 1200 meters.
1. Electrical characteristics of RS-485: Logic "1" is represented by + (2-6) V voltage difference between two lines; logic "0" is represented by - (2-6) V voltage difference between two lines. The interface signal level is lower than RS-232-C, so it is not easy to damage the chip of the interface circuit, and the level is compatible with TTL level, so it is convenient to connect with TTL circuit.
2. The maximum data transmission rate of RS-485 is 10Mbps
3. RS-485 interface is a combination of balanced driver and differential receiver, which has better anti common mode interference ability, that is, good anti noise interference.
4. The maximum communication distance of RS-485 is about 1219m, and the maximum transmission rate is 10MB / s. The transmission rate is inversely proportional to the transmission distance. Under the transmission rate of 100kb / s, the maximum communication distance can be achieved. If a longer transmission distance is needed, a 485 repeater needs to be added. Generally, the RS-485 Bus supports 32 nodes at most. If a special 485 chip is used, it can reach 128 or 256 nodes, and the maximum can support 400 nodes.
Because RS-485 interface has good noise immunity, long transmission distance and multi station capability, it becomes the preferred serial interface. Because the half duplex network composed of RS485 interface generally only needs two wires, so RS485 interface adopts shielded twisted pair transmission. The RS485 interface connector adopts the 9-core plug base of DB-9, the interface with the intelligent terminal RS485 adopts DB-9 (hole), and the keyboard interface RS485 connected with the keyboard adopts DB-9 (PIN).
RS422
RS-422 is differential mode transmission, with strong anti-interference ability. It can transmit 1200 meters, and RS232 can transmit up to 15 meters. The principle of RS422 bus is basically the same as that of RS485 and RS422, both of which are sent and received in differential mode, without digital ground wire. Differential operation is the fundamental reason for the long transmission distance under the same speed condition, which is the fundamental difference between RS232 and RS232, because RS232 is a single end input and output, at least three lines (asynchronous transmission) of digital ground wire, transmission line and receiving line are required for duplex operation, and other control lines can be added to complete the synchronization and other functions.
RS422 can work in full duplex mode without affecting each other through two pairs of twisted pairs, while RS485 can only work in half duplex mode, and can not work in both mode, but it only needs one pair of twisted pairs.
RS422 and RS485 can transmit 1142 meters at 19 kpbs. A new transceiver line can be used to connect devices.
One thousand three hundred and ninety-four
IEEE 1394, alias FireWire
- 【Printing】
- 【Collection】
- 【Return】
相关产品RELATED PRODUCTS
Address: No.28, southwest Lang Road, Henan Industrial Zone, Jinxia, Chang'an Town, Dongguan City, Guangdong Province