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[/vc_column_text][vc_tour][vc_tab title=”Serial port simply introduce” tab_id=”1393548851-1-39″][vc_column_text]Serial communication interface( Serial Interface) is referred to

that the data is transferred one by one in an order and the

communication line is simple .

As long as a pair of transmission lines ,the serial interface can

realize two-way  communication(can directly use telephone

lines as transmission line),which greatly reduces the cost.

The serial interface is especially suitable for long distance

communication, but the speed is slow which only 1 bit is transmitted at a time.[/vc_column_text][/vc_tab][vc_tab title=”The feature ” tab_id=”1393548851-2-17″][vc_column_text]Could be completed by one transmission line. The cost of serial is low but the speed is slow.The distance of Serial communication is range from a few meters to thousands of meters. According  to the transmitting direction of the information serial communication can divided into simplex, half-duplex and full-duplex.[/vc_column_text][/vc_tab][vc_tab title=”Several ways ” tab_id=”1393609320940-2-7″][vc_column_text]There are synchronous Serial communication mode and asynchronous serial communication mode.

Synchronous Serial refers to the SPI (Serial Peripheral interface), as the name suggests a Serial Peripheral interface.

Following is the picture of SPI data transmission processs

UART is a kind of chip which parallel input  and serial output, often integrated in the motherboard.

Electrical level of TTL is 3.3V, while RS232 is negative logic level,  +5~+12V is low

level, and -12~-5V is high level. MDS2710,MDS SD4,EL805 are RS232 interface[/vc_column_text][/vc_tab][vc_tab title=”The difference ” tab_id=”1393609322498-3-7″][vc_column_text]In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data andcontrol signals connecting between DTE (data terminal equipment) and DCE (data circuit-terminating equipment, originally defined as data communication equipment). It is commonly used in computer serial ports. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997.

An RS-232 serial port was once a standard feature of a personal computer, used for connections to modems, printers, mice, data storage, uninterruptible power supplies, and other peripheral devices. However, the low transmission speed, large voltage swing, and large standard connectors motivated development of the Universal Serial Bus, which has displaced RS-232 from most of its peripheral interface roles.^{[citation needed]} Many modern personal computers have no RS-232 ports and must use either an external USB-to-RS-232 converter or an internal expansion card with one or more serial ports to connect to RS-232 peripherals. RS-232 devices are still found, especially in industrial machines, networking equipment, and scientific instruments.

RS-422 (also EIA-422) is a technical standard that specifies electrical characteristics of a digital signaling circuit. Differential signaling can transmit data at rates as high as 10 million bits per second, or may be sent on cables as long as 1500 meters. Some systems directly interconnect using RS-422 signals, or RS-422 converters may be used to extend the range of RS-232 connections. The standard only defines signal levels; other properties of a serial interface are set by other standards.

RS-422 is the common short form title of American National Standards Institute (ANSI) standardANSI/TIA/EIA-422-B Electrical Characteristics of Balanced Voltage Differential Interface Circuits and its international equivalent ITU-T Recommendation T-REC-V.11,also known as X.27. These technical standardsspecify the electrical characteristics of the balanced voltage digital interface circuit.RS-422 provides for data transmission, using balanced, or differential, signaling, with unidirectional/non-reversible,terminated or non-terminated transmission lines, point to point, or multi-drop.

Several key advantages offered by this standard include the differential receiver, a differential driver and data rates as high as 10 megabaud at 12 metres (40 ft). The specification itself does not set an upper limit on data rate, but rather shows how signal rate degrades with cable length. The figure plotting this stops at 10 Mbit/s.The maximum cable length is 1500 m. Maximum data rates are 10 Mbit/s at 12 m or 100 kbit/s at 1200 m.

RS-485, is a standard defining the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. The standard is published by the Telecommunications Industry Association/Electronic Industries Alliance(TIA/EIA). Digital communications networks implementing the EIA-485 standard can be used effectively over long distances and in electrically noisy environments. Multiple receivers may be connected to such a network in a linear, multi-drop configuration. These characteristics make such networks useful in industrial environments and similar applications.

The EIA once labeled all its standards with the prefix “RS” (Recommended Standard), but the EIA-TIA officially replaced “RS” with “EIA/TIA” to help identify the origin of its standards.The EIA has officially disbanded and the standard is now maintained by the TIA. The RS-485 standard is superseded by TIA-485, but often engineers and applications guides continue to use the RS designation.

RS-485 enables the configuration of inexpensive local networks and multidrop communications links. It offers data transmission speeds of 35 Mbit/s up to 10 m and 100 kbit/s at 1200 m. Since it uses a differential balanced line over twisted pair (like RS-422), it can span relatively large distances (up to 4,000 feet (1,200 m)). A rule of thumb is that the speed in bit/s multiplied by the length in meters should not exceed 10⁸. Thus a 50 meter cable should not signal faster than 2 Mbit/s.

In contrast to RS-422, which has a single driver circuit which cannot be switched off, RS-485 drivers need to be put in transmit mode explicitly by asserting a signal to the driver. This allows RS-485 to implement linear bus topologies using only two wires. The equipment located along a set of RS-485 wires are interchangeably called nodes, stations or devices.

[/vc_column_text][/vc_tab][vc_tab title=”Hardware parameters ” tab_id=”1393609366471-4-10″][vc_column_text]1.The common mode output of the voltage

is different between the RS485 and RS422, RS485 is between

-7V to +12V, while the RS422’s voltage is between the -7V to 7V.

2.  RS485 receiver minimum inputting impedance is 12 k Ω, while RS – 422 is 4 k Ω.

3. Due to the RS485 contents all the standard of RS422, so the driver of RS485 can be

used in the application of RS422 network.

4.Both the RS485 and RS422, the maximum transmission distance is about 1219 meter

s and the maximum transmission rate is 10 MB/s.

Balanced twisted_pair cable length is inversely proportional to the transmission rate,

we can use the longest cable length under the 100 KB/s.

Only in a very short distance can get the highest rate of transmission.

The maximum transmission rate of 100 meters long twisted-pair cable is only 1 MB/s.[/vc_column_text][/vc_tab][/vc_tour][/vc_column][/vc_row]