Rs485 driver, in addition to the output states of 1 and 0. The increased load causes the rs485 transmitter to deliver more current into the load, which has the effect of reducing the differential output voltage developed by the driver ic. Standard rs422 drivers are guaranteed to source and sink a minimum 20 ma across a 100. Ds9638 1features description the ds9638 is a schottky, ttl compatible, dual 2 single 5v supply differential line driver designed specifically to meet schottky technology the eia standard rs422 specifications. This is a 4wire connection, one pair of twisted wires is used for receive, the other for transmit. Rs485 eiatia485 differential data transmission system. Q im using the adm3202aruz circuit in one of my designs.
To illustrate their basic differences, a condensed description of each standard is presented in the following subsections. The prl414rstr high speed fanout line driver facilitates testing and integration of high speed digital communications circuits. The output impedance can be split for many applications. Range extension model bb485opdrhs can be used to extend. The importance of termination resistor and its value is still unclear. Using a mosfet gate driver as a highvoltage line driver for. The device includes failsafe circuitry, guaranteeing a logichigh receiver output when receiver inputs are.
There are many way to terminate this signal and it depends on the characteristics of the device, in this case an ni 9411 digital input. The one driver limitation means that an rs422 bus is unidirectional, while rs485 can communicate bidirectionally over a single bus. Eiatia 422 defines a balanced differential interface. Eia485 devices may be used in 422 circuits, but eia 422 may not be used in 485 circuits because of the lack of an enable line. The only difference in hardware of the rs 485 and rs 422 circuits is the ability to set the output to high impedance state. An rs422 driver may have this signal, but it is not always required. When the driver is enabled, a logic low on di forces y low and z high, while a logic high on di forces y high and z low. These parts contain one driver and one receiver in half duplex configuration. Do you have any rs422 drivers and receivers capable of operating during the iec 644 electrical fast transient burst testing with no signal degradation. While the rs 485 specification does not specify cabling, these recommendations should be used for rs 485 systems as well. Care must be taken however, to ensure that the resistance connected in place of the load is able to dissipate sufficient power without damage. Rs422 receiver, ttl outputs, sma ios pulse research lab. A high level enables the driver differential outputs, y and z. In situations where data must be communicated over long distances and through electrically noisy areas, rs422 provides a higher reliability replacement for standards such as rs232.
The only difference in hardware of the rs 485 and rs 422 circuits is the ability to set the output to. The same analysis as above would yield a load of 34ohms if the cable is terminated on both ends with its characteristic impedance of 68ohms. Threestate outputs pnp high impedance inputs pia compatible fast propagation times typical 15 ns ttl compatible single 5. Rs485 allows 32 devices on the bus, in any combination of receivers and transmitters, while rs422 allows only one driver and up to 10 receivers. Guide to selecting and using rs232, rs422, and rs485. Guide to selecting and using rs232, rs422, and rs485 serial. Functional operation under these condition is not implied. April 4, 2007 rs485 rs422 and rs232 cable information. Rs 485 allows 32 devices on the bus, in any combination of receivers and transmitters, while rs 422 allows only one driver and up to 10 receivers. There are some major differences between rs485 and rs422. An example of a pullup and a pulldown resistor on an rs485 bus to ensure the proper voltages on an inactive bus.
Ds9638 rs422dual high speed differential line driver check for samples. Maxim offers a complete portfolio of interface devices. Eiatia422 defines a balanced differential interface. Rs485 eiatia485 differential data transmission system basics. Many include integrated features that reduce cost, design complexity, and board space by eliminating external components. Do you have any rs 422 drivers and receivers capable of operating during the iec 644 electrical fast transient burst testing with no signal degradation. Rs 422 will support pointtopoint, and multidrop circuits, but not multipoint. The rs485rs422 modes feature one driver and one receiver. Ds75176bds75176bt multipoint rs485rs422transceivers. Rs485 summary of key specifications parameter conditions min max units driver output voltage, open circuit 1. Eia485 devices may be used in 422 circuits, but eia422 may not be used in 485 circuits because of the lack of an enable line. Differential parallelterminated driver output waveforms.
The rs422 specification recommends 24awg twisted pair cable with a shunt capacitance of 16 pf per foot and 100 ohm characteristic impedance. Rs422, also known as tiaeia422, is a technical standard originated by the electronic industries alliance that specifies electrical characteristics of a digital signaling circuit. Differential driver output no load vod1 5 v 2 v differential driver output with load vod2 1. The rs 422 specification recommends 24awg twisted pair cable with a shunt capacitance of 16 pf per foot and 100 ohm characteristic impedance. Because a drivers output depends on the current it must supply into a load, adding transceivers and. Selecting and using rs232, rs422, and rs485 serial data. Differential rs485 transmissions figure 6 produce opposing currents and magnetic fields along each segment wire of a twistedpair cable, thus minimizing the emitted electromagnetic interference emi by cross. Isolation model bb485opdrhs provides 2 kv digital isolation with 8 kv air esd protection and 600 w transient voltage suppression on the data lines. Termination is used to match impedance of a node to the impedance of the. Il422 isolated rs422rs485 interface product datasheet. The bicmos output st age consists of a large nmos sink driver and a pmosnpn emitter follower source driver. Using the hs26ct31rh radiation hardened rs422 line.
The output impedance of an operational amplifier, often designated zo, arises from the fact that the output driver circuit and the associated connections have a defined impedance. The texas instruments sn65hvd37 ic used in this example includes a 3state enable input to force the two driver outputs into a high impedance state. Vod1 differential driver output io 0 5 v voltage unloaded vod2 differential driver output see figure 2 r 50 rs4223 2 v voltage with load r 27 rs485 1. Rs485rs422 circuit implementation guide analog devices. The il422 was the first isolated rs422 interface in a standard 16pin soic package to meet the ansi standards eiatia422b. The st485e is a low power transceiver for rs485 and rs422 communication. But since its dc levels i am reckoning it will be in the range of 6v and 0v.
The measurement of output impedance uses the same method as for input impedance but with different connections. This section summarises the key features of the ft232rq which apply to the usbrs422pcb. In situations where data must be communicated over long distances and through electrically noisy areas, rs 422 provides a higher reliability replacement for standards such as rs 232. Differential input threshold voltage of a receiver. There are some major differences between rs 485 and rs 422. How to properly configure and wire rs422 and rs485. This is a differential signal and requires transmission line termination. Radiation hardened cmos processing assures low power. Compared with rs 422, the higher input impedance and wider commonmode range of an rs 485 connection enables longer line lengths. For further details, and a full features and enhancements description consult the ft232r datasheet, this is available from. This represents the rs422 connections of a device, card or converter. Example of rs 485 communication cable beyond the network cabling, it is mandatory that the layout of printedcircuit boards and the connector pin assignments of rs 485 equipment maintain the electrical characteristics of the network by keeping both signal lines close and equidistant to another.
Vod change in magnitude of driver differential output voltage for 0. However, i can not find much information on the electrical characteristics of the 9411. Rs 422 s capabilities make it a good choice for extending the distance and speed of pointtopoint connections. The main difference between rs422 and rs485 is that while rs422 is strictly for pointtopoint communications and the driver is always enabled, rs485 can be used for multidrop.
Fullduplex, low power, slew rate limited, eia rs485. An oscilloscope or ac voltmeter is connected across the amplifier load e. I am purchasing an incremental encoder that has an rs422 line driver ouput. They usually contain one driver and one receiver in half duplex configuration. Figure 4 shows the crosssection of a fourpair, utp cable typically. Vdds 105 tdmax maximum delay from singleended input to rs422 output 30 ns digital outputs x4, x5, x6 201 isclo output short circuit lo channel as rs422 receiver 8 100 ma v vdds oen1 202 ischi output short circuit hi channel as rs422 receiver 100. Compatible rs485 receivers, transceivers, and repeaters are also offered to. Rs422 will support pointtopoint, and multidrop circuits, but not multipoint. The set up for measuring input impedance is illustrated in fig.
The prl414rstr high speed fanout line driver facilitates testing and integration of high speed digital communications circuits and distribution of satellite signals. The receiver also includes an enable signal equipment manufacturers could use to turn off the receiver. The differential input threshold voltage vth of a receiver is the. The lowpower, highspeed transceivers of this family are designed for rs485, rs422 and rs423 communication applications. I am purchasing an incremental encoder that has an rs 422 line driver ouput. Compared with rs422, the higher input impedance and wider commonmode range of an rs485 connection enables longer line lengths. The use of a differential driver permits reliable transmission of data over long distances in. Rs 422, also known as tiaeia 422, is a technical standard originated by the electronic industries alliance that specifies electrical characteristics of a digital signaling circuit.
Features, specifications, alternative product, product training modules, and datasheets are all available. Rs422 inputsensitivity test circuit and resultant waveform. If the enable signal is off, one can consider the driver as disconnected from the transmission line. Browse digikeys inventory of rs422, rs485 differential line driverrs422, rs485. Example of rs485 communication cable beyond the network cabling, it is mandatory that the layout of printedcircuit boards and the connector pin assignments of rs485 equipment maintain the electrical characteristics of the network by keeping both signal lines close and equidistant to another. If so, do you have any application notes and or evaluation boards. The load presented to an rs485rs422 driver is quantified in terms of the unit load, which is defined as the input impedance for one standard rs485 receiver 12k. Rs422 line driver to ni digital input termination ni. The device includes failsafe circuitry, guaranteeing a logichigh receiver output when receiver inputs are open or shorted. The driver or generator is labeled d, the receiver is labeled r, and the termination impedance is zt. In this case the amplifier load is replaced with the decade box or variable resistor. Rs485 standard conform drivers provide a differential output of a minimum 1.
Using a mosfet gate driver as a highvoltage line driver. This represents the rs 422 connections of a device, card or converter. Differential driver output skew tdskew figures 2, 3. Rs422, rs485 differential line driver texas instruments. The main difference between rs 422 and rs 485 is that while rs 422 is strictly for pointtopoint communications and the driver is always enabled, rs 485 can be used for multidrop. They both use the same differential drive with identical voltage swings. Thus, a standard rs485 driver is capable of driving 32 unit loads 32 12k. Model bb485opdrhs is a high speed, optically isolated rs422485 repeater that supports data rates up to 1. Rs422, rs485 receivers maxim integrated rs422, rs485. Rs422 systems can transmit data at rates as high as 10. An rs485 driver must have the enable control signal. February 2009 rev 16 119 19 st485b st485c low power rs 485rs 422 transceiver features low quiescent current. That could work but the 74hc14 has a vcc dependent logic input threshold so id have to level shift the input to get it to switch with 10v vcc. I also dont know what its actual output impedance is its rated something like 1v sag at 20ma, so it seems reasonable to say 50 ohm per driver in addition to the output resistance.
Balanced differential signals first, lets talk about advantages and disadvanteges of rs 422485. Low power rs 485rs 422 transceiver features low quiescent current. Smith serial communication products is your rs485 rs232 and rs422 authority for converters, repeaters, microprocessors, fiber optics, ethernet serial port server, ethernet serial products, mei, nodes and networks, usb, serial and digital io solutions, serial and analog io solutions including rs485, rs232, rs422, rs 485, rs 232, rs 422, telemetry, process control, translators, extenders. While the rs485 specification does not specify cabling, these recommendations should be used for rs485 systems as well. Sometimes you can see a rs 485 system in a point topoint system. Each driver output and receiver input is protected against electrostatic discharge up to 15 kv and has no latchup. Ds96172ds96174 rs485rs422 quad differential line drivers rev.
Differential rs 485 transmissions figure 6 produce opposing currents and magnetic fields along each segment wire of a twistedpair cable, thus minimizing the emitted electromagnetic interference emi by cross. A functional block diagram of this device is shown in fig. Ssi output provides effective synchronization in a closedloop control system. Each driver output and receiver input is protected against 15 kv electrostatic discharge h. Ds9638 rs422dual high speed differential line driver. The connections for two devices with receive and transmit rs422 signals is shown in figure 1. It was intended to replace the older rs 232c standard with a standard that offered much higher speed, better immunity from noise, and longer cable lengths. The connections for two devices with receive and transmit rs 422 signals is shown in figure 1. The il422 was the first isolated rs422 interface in a standard. Using the hs26ct31rh radiation hardened rs422 line driver.
564 1451 576 1468 406 669 814 20 41 998 1155 414 431 643 187 1487 1096 1607 1020 106 882 676 120 60 1443 756 1179 588 26 1053 1254 934 469 22 86 1410