jordan shoes women RS-232, RS-422 and RS-485 Stand

received, the originator of the data signal is relative to the signal ground, such as data sent from the DTE device using the DB25 connector is pin 2 relative to pin 7 (signal ground) level, DB25 pin definitions see Figure 1 of the . Typical RS-232 signal swing between positive and negative levels, when sending data, the transmitter driver output affirmative Ping +5 ~ +15 V, negative level at -5 ~-15V level. When no data transmission, the line for the TTL,low airmax shoes Dog 's life, discern the final pi, transfer data from the starting to the end line level from TTL level to RS-232 level and back to TTL levels. The receiver in a typical operating level +3 ~ +12 V and -3 ~-12V. Send and receive the level of the level distinction of only almost 2V to 3V, so the common mode refusal ability, coupled with the dispensed capacitance on the twisted pair, the maximum transmission distance of about 15 meters, the maximum rate of 20kb / s. RS-232 for point to point (that is, only a pair of sending and receiving equipment) communication and devise, its drive load 3 ~ 7kΩ. Therefore, for the local RS-232 communications between devices. Its relevant electrical parameters in Table 1.
provides RS232 RS422 R485
work single-ended differential differential
nodes 1 received, 1 sent 1, received a portly 32 fat 10 maximum transmission received
400 feet cable length of 50 feet 400 feet
maximum transmission rate of 20Kb / S 10Mb / s 10Mb / s
most drive output voltage of + / - 25V-0.25V ~ +6 V-7V ~ +12 V
driver output signal class (minimum load) load + /-5V ~ + / -15V + /-2.0V + /-1.5V
driver output signal level (no load maximum) load + /-25V + /-6V + /-6V
drive the load impedance (Ω) 3K ~ 7K 100 54
slew rate (maximum value) 30V/μs N / A N / A
receiver input voltage range of + /-15V-10V ~ +10 V ;-7V ~ +12 V
receiver input threshold of + /-3V + /-200mV + /-200mV
Receiver Input Resistance (Ω ) 3K ~ 7K 4K (minimum) ≥ 12K
drive common-mode voltage-3V ~ +3 V-1V ~ +3 V
the receiver common mode voltage of-7V ~ +7 V-7V ~ +12 V ;
Table 1
III, RS-422 and RS-485 reg code interface criterion
1. Balance Transfer
RS-422, RS-485 and RS-232 not the same, differential transmission of file signals, also known as poised transmission, it uses a couple of twisted-pair, which will be defined as the line A, the elucidation of the other line to B.

Typically, send drive A, B between the positively charged smooth in the +2 ~ +6 V, is a rational state, the negative level at -2 ~ 6V, is another rational state. There is also a signal to C, the RS-485 There is also a When the
the receiver and transmitter can also be relating to the provisions of income, start by balancing the corresponding tangled pair joined to the AA and BB, when the income side AB is greater than +200 mV between the levels, the output is logic level , less than-200mV, the output of negate logic levels. Receivers for balanced line-level range is ordinarily among 200mV to 6V.
6, RS-422 and RS-485 grounding problem
ground electronic systems are very major, but constantly ignored. Ground often lead to improper handling electronic reliability system can not even compromise a system. RS-422 and RS-485 ground transport network is also very major, because the grounding system unreasonably influence the reliability of the entire network, primarily in the working context is penniless and the transmission distance and circumstances, the requirements for the grounding more stringent. Otherwise, a high failure rate of the interface. In many cases, the connection RS-422, RS-485 communication interlock when simply using a twisted pair to each interface While ignoring the signal ground connection, which in many cases is the connection method can work, but it planted a lot of secret perils, which have the following two reasons:
1. Common-mode interference: As stated Qian Wenyi, RS-422 and RS-485 Interface signals are transmitted by way of difference, does not need relative to a reference point to find the signal,jordan shoes new release, the system only detect the potential difference between the two lines on it. But often overlooked transceivers have a certain common-mode voltage range, such as RS-422 common-mode voltage range of -7 ~ +7 V, the RS-485 transceiver common-mode voltage range of -7 ~ +12 V, only to encounter the above conditions, the entire network to work properly. Common mode voltage line when the network further this range will affect the stability of communication can be *, or even damage to the interfaces. To Figure 11, for example, when sending the drive A B send data to the receiver, the transmission output drive A common mode voltage VOS, since the two systems have detach grounding system, ground potential differences exist VGPD. Then, the receiver input common mode voltage VCM will approach the VCM = VOS + VGPD. RS-422 and RS-485 standards provide that VOS ≤ 3V, but may have very actual VGPD (more than ten volts or even tens of volts),nike air jordan retros, and may be accompanied by strong interference signals, causing the receiver common mode input VCM outside the normal range and interference in the transmission line current, ranging from affecting the normal traffic, ponderous damage to the communication interface circuit.

2. (EMI) problems: mail output signals steer the common mode chapter of the need for a return way, such for the return is no a low-resistivity aisle (signal floor), will return apt the form of radiation source, the entire bus will be like a mammoth antenna apt disperse electromagnetic waves.
For these reasons, RS-422, RS-485 balanced differential transmission although, but for the entire RS-422 or RS-485 network must have a low resistance to signal ground. A cheap resistance signal to the work of the two interfaces chained together, so namely common mode interference voltage VGPD is shorted. This added signal ground can be a line (unshielded twisted pair) or shielded twisted pair shield.
is worth noting that this approach is only forcible high impedance common mode interference type, for a massive source of interference resistance, short the ground will not form a great circulate current, the communication will not be greatly affected. When common mode interference source resistance is low, the grounding line formed in the great loop current, affecting the regular traffic. In my attitude, can take the following 3 measures:
(1) If the interference is not very small source resistance can be added in the grounding line current limiting resistor to restrict the interference current. Ground resistance may cause the increase of common-mode voltage increases, but at the peak of the fitting range of control will not affect normal communications.
(2) using drifting technique, hack off the ground loops. This is more commonly used method is very effective, when the common mode interference is very small interior resistance has been described above does not work, then you can consider the introduction of interference node (for example, poor working environment in the field device) movable up ( That is the system with the chassis or circuit ground separation), so hack off the ground loops, will not form a large loop current.
(3) the use of isolation interface. In some cases, for security or other considerations, the circuit to be connected with the chassis or the ground, not suspended, then the interface can be used to cut off the ground loop isolation, but should still have a ground to isolate the common side work with other interfaces connected to the ground.

VII, RS-422 and RS-485 network fail-safe
RS-422 and RS-485 standards are set the receiver threshold is ± 200mV. Such provisions can provide a relatively high ruckus rejection capability, as mentioned above, when the receiver A-level than high-level B or above +200 mV, the output is positive logic, and vice versa, the output is negative logic. However, the existence of a third state, that is the originator After sending the host a information in the data, the bus is placed in the third state, that is, there is no signal when the bus drive the bus,nike air jordan woman, so that the voltage between AB in the -200 ~ +200 mV Up to tend to 0V, which raises the question: receiver output state of uncertainty. If the receiver output is 0V, the network from the machine will interpret it as a current start morsel, and tried to read the follow-up of bytes,airmax 360, because there will not be stop morsel, resulting in a border error results, no device apply bus, network paralyzed state. Apart from the above mentioned two lines will cause the bus is idle less than 200mV dropout voltage situation, the open or short circuit will happen. Therefore, certain measures should be taken to avert uncertainty in the receiver.

normally biasing the bus when the bus is free or open, use discrimination resistors to bias the bus in a definite state (differential voltage ≥-200mV). Figure 13. Will be pulled to ground on the A, B down to 5V, the typical amount of resistor 1kΩ, the specific capacitance values ​​with the cable changes.
the upon method is more classic approach, but it still does not solve the problem of short-circuit the bus, some contractors will receive the threshold to shake -200mV/-50mV, solve the problem. For example, Maxim's MAX3080 series of RS-485 interface not only eliminates the need for external bias resistor, and to solve the bus short circuit protection in case of failure.
the use of four-wire articulation, and can only attain the same RS-422 multi-point communications, which can have merely one basic (Master) appliance and the recess from the device, yet it is one improvement over RS-422, regardless of four-wire bus or second-line connections can be received more than 32 devices.

RS-485 and RS-422 is still in its different common-mode output voltage is different, RS-485 is-7V to + 12V between the RS-422 in between-7V to +7 V, RS-485 Receiver minimum input impedance of 12k the knife Jian S-422 is a 4k; age Gap shoot transport S-485 meets all RS- 422 specification, so the RS-485 drive can be used in RS-422 network applications.
RS-485 electrical provisions of the relevant Table 1.
RS-485 and RS-422 as the maximum transmission distance is about 1219 meters, the maximum transfer rate of 10Mb / s. Balanced twisted pair transmission rate is inversely proportional to the length of the 100kb / s rate the following, it may use the provisions of the longest cable length. Only in a very short distance to get the highest rate of transmission. 100 m long twisted pair generally maximum transmission rate of only 1Mb / s.
RS-485 requires two termination resistors, the resistance required is equal to the characteristic impedance of transmission cable. In the moments when the distance transmission without terminating resistor, usually 300 meters without terminating resistor. Terminating resistor at both ends of the transmission bus.
four, RS-422 and RS-485 network installation points to note
RS-422 can support 10 nodes, RS-485 supports 32 nodes, so multiple nodes of the web. Matching web topology generally use the bus extremity structure, does not patronize ring or star networks. In creating a web, ought note the following points:
1. Using a twisted-pair cable for the bus, each node will be connected, to each node from the bus Lead length should be as short as feasible so that the pinout of the reflected signal minimal shock on the bus signals. Figure 8 shows the practical application of some common mistakes in the connection (a, c, e) and the right connections (b,-.九种会让你头晕的图,!, d, f). a, c, e Although the three network connection is not correct, a short distance,mauve nike shoes 上床之前，上床之后..., low rate is still likely to work, but with the extension of communication distance or communication rate boost, which will be build up serious detrimental effects, chiefly deserving to signal the end of each branch with the native signal is superimposed above reflection, will reason the signal quality.
2. Should be eminent that the continuity of the bus specific impedance, impedance discontinuity in the signal reflection occurs. The following are several positions that are not effortless to produce continuity: the alter partitions of the bus takes a differ cable, or a certain duration of transceivers on the bus there are also many crowded * with installation, addition is a long branch line leads to the bus.
short, should invest a unattached, continuous signal path as buses.
V, RS-422 and RS-485 transmission line matches the some of the directions
on RS-422 and RS-485 bus network generally use the terminating resistor matching. However, a short distance and low rates can not consider termination. So do not take into account the circumstances match? Theoretically, in the mid-point of each received data signal is sampled, by the time the reflected signal attenuation at the opening of sampling to be low enough to be considered can not match. But in reality difficult to clutch, the United States MAXIM company has an theoretical story that the conviction can be used to resolve what kind of data rate and cable length required to match: When the signal transitiin due time (ascend or fall period) More than one-way signal transmission according the bus more than 3 times the time necessary can be no match when. For example, functions a slew MAX483 RS-485 interface, the output signal rise or fall time of a minimum of 250ns, typical twisted pair signal transmission rate of about 0.2m/ns (24AWG PVC cable), then as long as the data rate in 250kb / s among the cable length does not surpass 16 meters, using MAX483 RS-485 interface as can be no end to match.
termination by the general method of terminating resistors, Qian Wenyi said, RS-422 remote bus cable and resistor, RS-485 should be in the beginning and end of the bus cable are required, and then terminating resistor . Terminating resistor is generally RS-422 network to take 100Ω, the RS-485 network access 120Ω. Equivalent to the cable characteristic impedance of the resistance, because most of the characteristic impedance of twisted pair cable is about 100 ~ 120Ω. This matching method is simple and effective, but there is a disadvantage, matching resistance to high power consumption, more stringent limits for the power system is not suitable.
Another path is to liken the matching power RC match, as shown in Figure 9. Cut off by a capacitor C DC makeup can save most of the power. However, the value of capacitor C is a tough, need to match in power and concession between the quality.
there is a matching method using diode, as shown in Figure 10. This procedure has at present real Energy-saving efficacy is noteworthy.

8, RS-422 and RS-485 transient protection
signal ground previously mentioned fathom, only the low frequency common mode interference protection for high frequency transient interference can not do anything. Because of the high frequency signal transmission line is equivalent in terms of inductance, so for the high-frequency transient interference, the substantial equivalent to the open ground. Although such short duration transient interference, but there may be hundreds or thousands of volts.
practical applying still exist under the likelihood of high-frequency temporary commotions. Usually in the high-power inductive loads such as switching motors, transformers, relays, etc., or speedy process will have a lofty rate of temporary interference, if I were you properly conservation will damage the RS-422 or RS-485 communication interface. This can be used for transient interference means to isolate or ignore conservation.
1. Isolation methods. This program is really transferred to the transient high-voltage electrical isolation barrier interface, due to the high isolation floor of insulation resistance and will not produce damaging surge current protection of the interface activity a character. Usually high-frequency transformers, optocouplers and other components to achieve access.
2. RS-422 electrical standard requirements
RS-422 full name is Figure 5 is a typical four-wire RS-422 interface. In fact there is a signal ground, a absolute of five lines. Figure 4 is the DB9 connector pin definitions. Since the receiver sends high input impedance and drive more drive capability than the RS232, it allows multiple receive the same transmission line connecting nodes, up to 10 nodes can be connected. That is, a main (Master), the rest is from the device (Salve), from the device can not communicate, so the RS-422 supports multi-point two-way communication. Receiver input impedance of 4k, so the originator of the maximum load capability is 10 × 4k +100 Ω (terminating resistor). RS-422 four-wire interface, the use of separate transmit and receive channels, so you do not control the data direction, the device must be the signal of anybody commute between the both can be in software (XON / XOFF handshaking) or in hardware (a pair of separate two- wire).

RS-422 the maximum transmission distance is 4000 feet (1219 meters), the maximum transfer rate of 10Mb / s. The balance of the length of twisted pair transmission rate is inversely proportional to the 100kb / s rate underneath the maximum transmission distance is possible. Only in a very short distance to get the highest rate of transmission. 100 m long twisted pair usually can get on the maximum transmission rate of only 1Mb / s.
RS-422 requires a termination resistance, requiring that their resistance is approximately equal to the characteristic impedance of transmission cable. In the moments when the distance transmission without terminating resistor, usually 300 meters without terminating resistor. Terminating resistor connected to the transmission cable of the most remote.
RS-422 aboard electrical parameters in Table 1
3. RS-485 electrical codes
the RS-485 RS-422 is amplified on the basis, so many electrical RS-485 RS-422 and similar provisions. If a balanced transmission are always needed in the transmission line terminating resistor connected and so on. RS-485 can be used with the four-line wire, two wire can achieve true multi-point two-way communication.
1, RS-232, RS-422 and RS-485 Origin
RS-232, RS-422 and RS-485 serial data interface is standard, initially by the Electronic Industries Association (EIA) developed and published, RS-232 released in 1962, appointed for the EIA-232-E, as the industry standard to ensure compatibility between productions from different manufacturers. RS-422 evolved from the RS-232, which is to recompense for the lack of RS-232's. RS-232 communications to enhance the short distance, low rate of defects, RS-422 communication interface defines a balance, the transfer rate of up to 10Mb / s, transmission range amplified to 4,000 feet (rate of less than 100kb / s), the and allow on the bus on a balance of up to 10 receivers. RS-422 is a single send, receive one-way multi-machine, balance transfer standard, was named TIA/EIA-422-A standards. In mandate to expand the range of application, EIA and in 1983 on the basis of the RS-422 RS-485 standard developed to increase multi-point,jordan shoes women, two-way communication skill, which allows multiple transmitters connected to the same bus, meantime increasing the transmitter drive capability and protection features of conflict, extended common mode range of the bus, named behind the TIA/EIA-485-A standards. The EIA recommendations are based on the standard
RS-232, RS-422 and RS-485 standard only on the electrical characteristics of the interface to make provisions, not narrated to connectors, cables, or accession, on this basis, users can build their own high-level communication protocol. Therefore, the application of the video industry, many manufacturers have built a high-level communication protocol, or the exclusive use of public or manufacturers. VCR manufacturers such as Sony and Panasonic in the RS-422 VTR control protocol is different, the video server control protocol is more, such as Louth, Odetis agreement is open, and ProLINK is based on the Profile.
II, RS-232 serial interface RS-232 standard
new PC, and communication is the maximum widely secondhand in manufacture as a serial interface. RS-232 is defined as a low-speed serial communication in increasing communication distance of the single-ended standards. RS-232 to unbalanced displacement mode, the so-called single-ended communication.