485 communication interface and 232 interface difference

pressure gauge Receiver common mode voltage – 7 v ~ + 7 v – 7 v ~ + 12 v
Accept, incipient data signal is relative to the signal, such as a data from the DTE equipment in use DB25 connector is 2 feet relative 7 feet (signal) level. The typical RS – 232 signal in positive and negative level swing between, in sending data, sending end driver output is level in + 5 ~ + 15 v, negative level in – 5 ~ 15 v level. When many according to transmission, online for TTL from the beginning, transmit data to the end, online level from the TTL level to RS – 232 level back to the TTL level. Receiver typical work level in + 3 ~ + 12 v and – 3 ~ 12 v. Due to send level and receiving level difference is only 2 v to 3 v or so, so the common mode rejection ability difference, plus twisted-pair cable distribution of capacitance, the maximum transmission distance about 15 meters, the highest rate of 20 KB/s. RS – 232 is to point to point (i.e. use a pair of collect, hair equipment) communication and design, which drive load for 3 ~ 7 k Ω. So the RS – 232 is suitable for local of communication between the equipment. The relevant electrical parameters see the table below.
RS – 485 need two terminating resistance, its value is equal to the requirements of cable transmission characteristic impedance. In the moment distance transmission not be terminating resistance, namely is in commonly 300 m below does not need to terminating resistance. Terminating resistance after the transfer of the ends of the bus.
Drive common mode voltage – 3 v ~ + 3 v – 1 v ~ + 3 v
RS – 422 need a terminating resistance, ask its resistance is about equal to the characteristic impedance of the transmission cable. In the moment distance transmission not be terminating resistance, namely is in commonly 300 m below does not need to terminating resistance. Terminating resistance meet in a transmission cable farthest end.
Receiver input voltage range + / – 15 v – 10 v ~ + 10 v – 7 v ~ + 12 v
Driver output signal level (load minimum) load + / – 5 V ~ + / – 15 V + / – 2.0 V + / – 1.5 V
Node number 1 charge, 1 1 hair 10 accept 1 hair and accept
RS – 485 and RS – 422 different also lies in its common mode output voltage is different, RS – 485 is – 7 v to + 12 v between, and RS – 422-7 v to + 7 v between, RS – 485 receiver minimum input impedance is 12 k, RS – 422 is 4 k; RS – 485 meet all RS – 422 standard, so the RS – 485 drive can be used in RS – 422 network application.
Receiver input resistance (Ω) 3 k ~ 7 k 4 k (minimum) or 12 k
Working way single end difference difference
RS – 422, the RS – 485 and RS – 232, data signal the differential transmission mode, also called balance transmission, it USES A pair of twisted pair, will be one of the line is defined as A, another line defined as B.pressure gauges
RS – 422 standard full name is “balanced voltage digital interface circuit of the electric property”, it defines the characteristics of interface circuit. In fact have a root signal ground, a total of 5 root line. Due to the receiver using high input impedance and send drive than RS232 stronger driving ability, so allow in the same on transmission line connecting multiple receiving node, most may meet 10 node. That is a main equipment (Master), the rest from equipment (Salve), from equipment can communication between, so the RS – 422 support point to many two-way communication. Receiver input impedance is 4 k, the inchoation maximum load capacity is 10 x 4 k + 100 Ω (terminating resistance). RS – 422 four wire interface due to using a separate the sending and receiving channel, so don’t control data direction, each device must be between any of the signal exchange all can by software methods (XON/XOFF shake hands) or hardware methods (a pair of single twisted-pair cable) to realize.
Three, RS – 422 and RS – 485 serial interface standard
RS – 422 maximum transmission distance for 4000 feet (1219 meters), the maximum transmission rate for 10 MB/s. The balance twisted-pair cable length and transmission rate is inversely proportional, in 100 KB/s rate the following, is it possible to achieve maximum transmission distance. Only in a short distance to obtain the highest rate transmission. General 100 meters long twisted pair on can get the biggest transmission rate is only 1 MB/s.pressure gauge
Normally, send drive A and B are level between in + 2 ~ + 6 v, is A logic state, negative level in – 2 ~ 6 v, is another logic state. Otherwise a signal ground C, in the RS – 485 have a “that can” end, but in the RS – 422 this is available but unused. “That can” end is used to control sending drive and transmission line cutting and connection. When the “that can” end work, send drive in a high impedance state, called “the third state”, namely, it is different from the logic “1” and “0” the third state.
At present RS – 232 is PC machine and communication industry the most used one kind of serial interface. RS – 232 is defined as a kind of low speed serial communication adding communication distance single-ended standard. RS – 232 take unbalanced transmission mode, namely so-called single end communication.
RS – 232, the RS – 422 and RS – 485 standard docking port only the electrical characteristics make regulations, and does not involve connectors, cable or agreement, and based on this, the user can set up their own top communication protocol. Therefore in the video industry application, many manufacturers have established a set of high-level communication protocol, or public or manufacturer exclusive use. Such as video manufacturer of Sony and panasonic for video of the RS – 422 control protocol is a difference, video server control protocol is more, such as Louth, Odetis protocol is open, and ProLINK is based on the Profile.
1. Balance transmission
Maximum transmission cable length 50 feet 400 feet of 400 feet
RS – 232, the RS – 422 and RS – 485 are serial data interface standard, originally is the electronic industries association (EIA) develop and release, RS – 232 released in 1962, named EIA – 232 – E, as the industry standard, to ensure that different manufacturer between products compatible. RS – 422 by the RS – 232, it is in order to make up for the shortage of RS – 232 and proposed. In order to improve the RS – 232 communication distance is short, low rate of faults, RS – 422 defines a balance communication interface, the transmission rate increased to 10 MB/s, transmission distance extended to 4000 feet (rate below 100 KB/s), and allow a balance bus connection a maximum of 10 receiver. RS – 422 is A kind of single sending and receiving machine of unidirectional, balance transmission standard, was named the TIA/EIA – 422 – A standard. To expand the scope of application, and EIA in 1983 in RS – 422 basis to develop the RS – 485 standard, increased the multipoint, two-way communication ability, namely allows multiple transmitter connected to the same line of bus, but also increase the transmitter driver ability and conflict protection feature, expands the bus common model circumference, named after TIA/EIA – 485 – A standard. Due to the EIA suggested standard are “RS” as a prefix, so in the communications industry, still used the standard to RS for address prefix.
And the four wire connection, and RS – 422 can only achieve point to more communication, namely can only have a primary (Master) equipment, and the rest from equipment, but it has the improvement than the RS – 422, whether four line or two wire connection mode can be more bus from 32 equipment.
RS – 485 and RS – 422, the maximum transmission distance is about 1219 meters, maximum transmission rate for 10 MB/s. Balance twisted-pair cable length and transmission rate is inversely proportional, in 100 KB/s rate the following, can only use regulation the longest cable length. Only in a short distance to obtain the highest rate transmission. General 100 meters long twisted pair maximum transmission rate is only 1 MB/s.
Pendulum rate (maximum) 30 v/μ s N/A N/A
Maximum transmission rate 20 KB/S 10 MB/S 10 MB/S
RS – 422 relevant electrical parameters see table 1
Due to the RS – 485 from RS – 422 on the basis of the development, so the RS – 485 many electric regulation and RS – 422 similar. If all the use of balanced transmission mode, all need in transmission line connected to the terminating resistance, etc. RS – 485 can use two line and the four line way, two wire can realize real multipoint two-way communication.
Driver output signal level (light maximum) light + / – 25 v + / – 6 v + / – 6 v
Maximum driving output voltage + / – 25 V – 0.25 V ~ + 6 V – 7 V ~ + 12 V
2. RS – 422 electric regulation led-torch
Drive load impedance (Ω) 3 k ~ 7 k 100 54
Receiver input threshold of + / – 3 v + / – 200 mv + / – 200 mv
Provisions RS232 RS422 R485
RS – 485 relevant electrical provisions refer to table 1.
3. RS – 485 electric regulation
The receiver will be and sending end relative regulation, accept, inchoation through the balance twisted-pair cable will AA and BB correspondence is linked together, when at the end AB between more than + 200 mv electricity at ordinary times, output is logic level, less than – 200 mv, output negative logic level. Receiver receive balance online level range usually in 200 mv to 6 between v.
Second, the RS – 232 serial interface standard

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