- Condition: New
- Brand: CHESHING
- Model: RS485 card
For the room, through the 485 protocol to communicate with the RDU-A, issued a communication signal, for UPS, air conditioning and other equipment, alarm monitoring its operation and machine control its automatic shutdown, automatic boot call.
RS485 protocol RS-232 and RS-422 converter between principle and connection prefix = o ns = 'urn: schemas-microsoft-com: office: office'
We usually for video servers, video recorders, switchers and other direct broadcast switching control of major use serial port, the main use of the RS-232, RS-422 and RS-485 control three interfaces. Here's serial interface standards and the use and external plug and cable are discussed.
RS485 communication protocol RS-232, RS-422 and RS-485 standard only on the electrical characteristics of the interface make provisions without involving connectors, cables or agreement, on this basis, the user can create their own high-level communication protocols such as: video servers RS422 serial communication with multiple interfaces, each can be achieved through the RS422 communication line is controlled by an external computer recording and playback. In addition to providing a variety of video server hardware control interface, but also provides protocol interfaces such as RS422 interfaces In addition to supporting RS422 outside the Profile protocol, also supports Louth, Odetics, BVW, etc. via RS422 control protocol.
RS-232, RS-422 and RS-485 serial data interface is standard, are developed by the Electronic Industries Association (EIA) and published, RS-232 released in 1962. RS-422 by the RS-232 development years, to improve the RS-232 communication distance is short, low rate of defects, RS-422 communication interface defines a balance, transfer rate up to 10Mbps, to extend the transmission distance of 4000 feet (at a rate lower than 100Kbps) to, and allow a bus connected to the balance up to 10 receivers. RS-422 is a single send, receives more than one way, the balanced transmission standard, was named TIA / EIA-422-a standard for the expansion of the scope of application, EIA and in 1983 enacted in RS-422 based on the RS-485 standard, an increase of multi-point, two-way communication capability, which allows multiple transmitters connected to the same bus, while increasing the transmitter drive capability and inrush protection characteristics, common-mode range extends the bus, named after the TIA / EIA485-a standard.
RS485 communication protocol 1. RS-232 serial interface standard
RS-232 is currently the PC and communications industry's most widely used serial interface. RS-232 is defined as a single-ended standards increase communication distance at a low speed serial communication. RS-232 unbalanced take transmission, the so-called single-ended communication. received, the originator of the data signal is a signal with respect to the typical RS-232 signal swings between positive and negative levels, when data is transmitted, the sender driver output positive level at + 5 ~ + 15V, negative level in 5 ~ -15V level. when there is no data transmission line for the TTL, start sending data to the end of the line level from TTL level to RS-232 level and then return
TTL level receiver in a typical operating level + 3 ~ + 12V and -3 ~ -12V. Since the transmission level and the reception level difference is only about 2V to 3V, so the common mode rejection ability, then plus the distributed capacitance on the twisted pair, the maximum transmission distance of about 15 meters, the highest rate of 20Kbps. RS-232 is a point to point (that is, only a pair of sending and receiving device) communication and design, and its drive load 3kΩ ~ 7kΩ. Therefore, RS-232 for local communication between devices.
RS485 communication protocol 2. RS-422 and RS-485 serial interface standard
(1) balanced transmission
RS-422, RS-485 and RS-232 are not the same, the data signal differential transmission, also known as balanced transmission, which uses a single twisted pair, which will be defined as the line A, another line is defined as B. Typically By sending drive a, B between the positive level + 2 ~ + 6V, is a logical state, negative level at -2V ~ 6V, is another logic state. There is also a signal to C, the RS-485 there is also an 'enabling' end, while in the RS-422 in which is may or may not 'enable' end is used to control the disconnection and connection to send the drive and transmission lines. when the 'enable' reach for the role, send the drive is in a high impedance state, known as 'third state', that it is distinct from a logic '1' and '0' a third state.
(2) RS-422 electrical regulations
Since the receiver sends high input impedance and drive stronger than RS232 drive capability, it allows the same transmission line connected to a plurality of receiving nodes, can connect up to 10 nodes. That is a main device (Master), the rest is from the device ( Salve), from no communication between devices, so the RS-422 supports two-way point-to-many communication. RS-422 four-wire interface thanks to separate transmit and receive channels, so you do not control the direction of data between the devices any necessary handshake can be by way of software (XON / XOFF handshaking) or in hardware (a separate pair of twisted-pair) to achieve. RS-422 maximum transmission distance of 4000 feet (about 1219 meters), the maximum transfer rate of 10Mbps. its the length of balanced twisted pair transmission rate is inversely proportional to the rate at 100Kbps or less, it may reach the maximum transmission distance. only a short distance to get the highest rate of transmission. on ships 100 m long twisted pair that can be obtained the maximum transfer rate of only 1Mbps. RS-422 requires a terminating resistor, asking them about the resistance equal to the characteristic impedance of the transmission cable. in the moment distance transmission without terminating resistor, which is generally at 300 meters without terminating resistor . terminating resistor connected to the distal end of the transmission cable.
(3) RS-485 RS-485 electrical regulations due from RS-422 developed on the basis of so many electrical RS-485 and RS-422 similar provisions as are balanced transmission mode, the transmission line connection is required terminating resistors, etc. RS-485 can be used with two-wire four-wire, two-wire system can achieve true multi-way communication. RS-485 bus, requiring communication distance of tens of meters to 1000 meters, widely used RS- 485 serial bus standard. RS-485 uses differential balanced send and receive, and therefore has the ability to suppress common mode interference. plus bus transceiver with high sensitivity, can detect voltage as low as 200mV, so the transmitted signal can be outside in km restored. RS-485 half-duplex mode, at any time only one thing in the sending state, therefore, the transmission enable signal circuit shall be controlled. RS-485 for multi-point interconnection is very convenient, you can save away many of the signal line. RS-485 can be networked applications constitute a distributed system, which allows up to 32 parallel drive and 32 receivers. RS-485 and RS-422 is different also in its common mode output voltage is different, RS -7V is between -485 to + 12V, while the RS-422 between -7V to + 7V; RS-485 meets all RS-422 specifications, the RS-485 drive can be used in RS-422 network applications . RS-485 and RS-422 as its maximum transmission distance is about 1219 meters, the maximum transfer rate of 10Mbps. inversely proportional to the length of the balanced twisted pair transmission rate, the rate at 100Kbps or less, it is possible to use a predetermined maximum cable length. only a short distance to get the highest rate of transmission. in general, 100 meters long and twisted pair maximum transmission rate of only 1Mbps.
(4) RS-422 and RS-485 network installation points to note
RS-422 can support 10 nodes, RS-485 supports up to 32 nodes, and therefore constitute a multi-node network. Network topology commonly used termination of the bus structure does not support ring or star network. When building a network, observe the following points:
* Use a twisted pair cable for the bus, each node will be connected in series, from the bus to each node Lead length should be as short as possible, so as to lead the reflected signal bus signals with minimal impact.
* Note that the continuity of the characteristic impedance of the bus, in the impedance discontinuity signal reflection occurs following situations easy to produce such a discontinuity: the different sections of the bus using a different cable, or on the bus have a certain period too close together transceiver installation, addition is long branch line leads to the bus. in short, it should provide a single, continuous signal path as a bus