1, RS232 is usually nine-pin, RS422 is generally only connected to four-wire communication, RS485 is usually used with two shielded stranded wire communication, there is no need for nine-pin interface.
2, signal labeling is from the perspective of DTE equipment, TD, DTR and RTS signals are generated by DTE, RD, DSR, CTS, DCD and RI signals are generated by DCE. The RS-232 port of the PC is a 9-core pin socket. Some devices are connected to PCSThe RS-232 interface, because the other party's transmission control signal is not used, only three interface lines are needed, namely, "transmit data TXD", "receive data RXD" and "signal ground GND".
3, this is called half duplex. 422 is full-duplex, that is, a person can speak while still listening. This is the difference between RS232 and RS485 in communication function. RS232 is mainly used for close equipment communication and is not suitable for long-distance field communication. That's why old computers have 232 ports. At that time, the 232 interface was mainly a card reader, magneticStation control, system cascade, etc. < / p > < h2 id = 'serial interface hardware category -- what is 232/422/485' > serial hardware category - what are 232/422/485 < / h2 >
1. Serial port and COM port refer to the physical interface (hardware). TTL, RS-23RS-485 refers to the level standard (electrical signal). Level standard (electrical signal). TTL level standards are: low level 0, high level 1 (to ground, standard digital circuit logic). RS485: positive level is 0, negative level is 1 (to ground, plus or minus 6-15V can be used, even in high resistance state).
2, RS-422 (EIA RS-422-a Standard) is A serial port connection standard for Apple Macintosh computers. RS-422 uses differential signals, and RS-232 uses signals from non-equilibrium reference points. Differential transmission uses two wires to send and receive signals, which offers better noise resistance and a longer transmission distance than RS-232. Better noise resistance and longer transmission distances are a big advantage in industrial environments.
3, RS-232, as the earliest standard, is used for short-distance (within 13 meters) serial port connections between devices. The choice of baud rate is crucial to the transmission distance and anti-interference, usually using the 5 line, the standard configuration can be within 3 meters. Its limitations mainly lie in the single point of communication, and it does not support multi-device networking.
1, HYM48HYM48HYM48HYM487-HYM491 and HYM1487 are low power for RS-485 / RS-422 communicationLossy transceiver. The HYM48HYM488 and HYM489 feature swing rate limited drivers that reduce EMI and reduce reflections caused by improperly terminal-matched cables for error-free data transfer of up to 250kbps.
2, application: the chip as a differential driver chip, each channel output a set of complementary Y, Z signals. This group of signals can be directly connected to other differential receiver chips for signal conversion and transmission. Post-drive can also be performed, such as drive optocoupler.
3, rs422 to ttl levelThe pendulum rate is not limited, and the transmission rate of up to 5Mbps422 interface chip can be achieved.
2, but because RS-485 often has to communicate with the RS-232 port of the PC 422 interface chip, it is actually generally up to 112Kbps. And because too high a rate will reduce the transmission distance of RS-485, it is often about 9600bps or below. The RS-422 has a maximum transmission range of 4,000 feet (about 1,219 meters), the largestThe transfer rate is 10Mb/s.
3, for example, the minimum rise or fall time of the output signal of the MAX483 RS-485 interface with limited slope characteristics is 250ns, and the signal transmission rate on a typical twisted pair is about 0.2m/ns (24AWGPVC cable), so long as the data rate is within 250kb/s and the cable length does not exceed 16 meters, When MAX483 is used as the RS-485 interface, no terminal matching can be added.
4, support RS422 interface core chip (MAX488, MAX490422 interface chip ; MAX489, MAX491) RS422/RS485 interface chip is known as follows 422 interface chip : Product comparison: RS422 is a four-wire dual port (two-wire receiving port and two-wire sending port). There's only one owner. The sending port of the host is connected to the receiving port of all the slaves. The receiving port of the host is connected to the sending port of all the slaves. As a result, slaves could not communicate with each other.
5, the interface signal level value is high, easy to damage the interface circuitBecause the chip is incompatible with the TTL level, it needs to use a level conversion circuit to connect with the TTL circuit. (2) The transmission rate is low, in the asynchronous transmission, the baud rate is 20Kbps. (3) The interface uses a signal line and a signal return line to form a common ground transmission form, which is easy to produce common mode interference, so the anti-noise interference is weak.
6, the electrical characteristics of RS-485: logic "1" is expressed by the voltage difference between the two lines as (2~6) V; The logical "0" is represented by the voltage difference between the two lines as - (2 to 6) V. Interface signalIf the level is lower than RS-232-C, it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level, which can be easily connected with the TTL circuit. The RS-485 has a maximum data transfer rate of 10Mbps.