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In this case, of course, the characteristics of the microcircuit must fully comply with the requirements of the standard. In TCP communication, configuration must be done at both ends of the communication. It is important to implement remote control and other requirements where serial ports must be tightly connected with Ethernet or fiber optic communications. Therefore, with the development of the times and the advancement of technology, devices that convert serial signals into Ethernet signals have emerged: from RS232/485 to RJ45 serial servers. RS-485 is known to be the advancement of RS-232 that supports technological upgradations. RS-485 figure 2 shows a generator (driver) with two interface connection points labeled "A" and "B". 1.The interface signal level is relatively high, and the interface circuit chip is easily damaged. 1) The signal level of the interface is relatively high, and the chip of the interface circuit is easily damaged. 3) The maximum transmission distance standard value of the RS485 interface is 4000 feet, but it can actually reach 3000 meters. 1. RS485 adopts balanced transmission and differential reception, has good anti-interference ability, and the signal can be transmitted for thousands of meters. With RS-485 communication, 1s and 0s propagate as a differential voltage.

RS-485 is specified to handle up to 100Mbps and is most suitable in industrial applications for transmitting information from actuators or card readers. This means that low data rates can handle an improperly terminated (or even unterminated) cable better than high data rates. This will cause reflections both back to the driver and forward to other receivers on the cable. They will be exactly backwards. The ringing occurs when the data transitions, and will eventually damp out. This phenomenon will appear as ringing on the edges of the signal. This installation does not require a third wire, but including one will not hurt. Since the laptop has no connection to earth ground, there will normally be little current through this third wire. Some handbooks say "use this wire for reference ground and earth the screen at one end only". For example; EIA-449 and EIA-530 are connector standards that reference RS-422 for electrical levels. They are in an electrically noisy environment, i.e. welding, motors starting and stopping, and other large electromagnetic sources. However, with the rapid development of today's science and technology, a large amount of information and communication data increases, and the requirements for distance are also increasing. For multiple connections they cannot use I2C as it is distance limited to about 1 meter.

It is incompatible with TTL level, so it needs to use level conversion circuit to connect with TTL circuit. It is not a simple conversion between the physical layer and the data link layer. In general, a serial port is a UART, and actually only defines the data link layer specification, namely start bits, data bits, and stop bits. If divided into ISO's 7-layer model (physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer), the serial port actually only includes the physical layer and data link layer. A serial port for long-distance communication that can transmit data over kilometers. Depending on the action mode, it is related to connection, shutdown, monitoring, etc. This is the part that needs to be dealt with after converting the serial port to a network port. 3.The two-wire RS485 can only work in a semi-duplex mode, and the sending and receiving cannot be carried out at the same time. The above figure shows the typical network connections for half-duplex (two-wire) RS-485 implementations. With 2 pairs of wires -- a dedicated "transmit" pair and a dedicated "receive" pair (similar to some Ethernet hardware), software can't tell the difference between RS-485 and RS-232.

Twisted pairs in RS485 communication however adds immunity which is a much better way to fight noise. There is a similar family of NOMAK cables which has only a common screen for all the pairs (individual pairs in the cable are unshielded). A shielded cable may be used. They want to run over CAT-5 (Ethernet) cable so they can use existing wiring. 200mV as undefined, but the IC manufacturer can put the threshold for a 0 and a 1 anywhere they want. You can see the resulting waveform below. This "current" driven principal is how an 4-20 milliampere analog signal can work over 100’s of feet. The RS485 standard (TIA-485) specifies differential data transmission over a terminated twisted pair.. Both methods ensure that the bus maintains a logical high state, corresponding to a positive differential voltage. In addition, the bus transceiver has high sensitivity and can detect the voltage as low as 200mV, so the transmission signal can be recovered beyond a kilometer.