The converter does not require a driver or any other software as it uses the max491 processor chip. Eiatia422 defines a balanced differential interface. Now, if i understand it correctly line a if more positive than line b, then the reciever outputs a logic 1 and vice. Competitive prices from the leading rs232, rs485, rs422 drivers transmitters distributor. 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. Output driver calibration also allows board designers to compensate for variations in trace impedance and termination voltage caused by manufacturing and assembly processes. Incremental pulse direction choose a before b or b before a device programmability is very significant for distributors, system integrators or machine builders since it helps them. Maxim offers over 160 rs485rs422 transceivers for applications such as automotive, hvac, metering, and point of sale pos. Converts 4 channels unbalanced rs232 signals to balanced rs422 signals.
The number of output lines, the type of interface driver ic, and the state of the output lines are important considerations. Cmos outputs cmos is an acronym for complementary metal oxide semiconductor which indicates that the device has been constructed of both pchannel and nchannel transistors. This is a differential signal and requires transmission line termination. We plan to use this card for serial io anyway and my understanding of this device is that there is a uart behind the rs422 interface and the outputs will either be tristated or if biased be in a highlow state when idle. The unit is not reliant on port power so you do not have to worry about the rs232s ability to. A receiver that provides failsafe for an open input condition, may provide failsafe for idle drivers output idle and tristate drivers output disabled conditions if the bus is not parallel terminated. Now, consider a driver rs422 connected to a reciever. Rs422 allows the direct connection of intelligent devices, without the need of modems. The output voltage is open initially without load as opencircuit voltage v 1 switch is open, that means r load is infinity and then measured as v 2 under load with r load at point in switch is closed. Technical description the data is coded as a differential voltage between the wires.
This allows one central control unit to send commands in parallel to up to ten slave devices. Rs485 networks can also operate using 2 pairs of wires, in fullduplex mode, as described for rs422. If the enable signal is off, one can consider the driver as disconnected from the transmission line. Some explanation of these concepts is included, but if the reader is unfamiliar with these areas, some additional study may be required. The output impedance of a device can simply be determined. This is a 4wire connection, one pair of twisted wires is used for receive, the other for transmit. Now, imagine the driver sends out voc 2v the differential voltage. 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. Absolute maximum ratings 12 value unit supply voltage, vcc 7 v. Ds3695, ds3695t, ds3696, ds3697 1features description the ds3695, ds3696, and ds3697 are high speed 2 meets eia standard rs485 for multipoint bus transmission and is compatible with rs422 differential tristate busline. Rs422, rs485 line driver maxim integrated rs422, rs485. Each line of the differential output will swing between 0 and almost 5v, and thats what a ttl compatible input needs. The program can create a data flow, wrap it to data packets rs232, tcpip or udp and send to a port. Rs422, rs485 differential line driver texas instruments.
These monolithic quadruple differential line drivers with 3state outputs are designed to meet the requirements of ansi standards eiatia422. Balanced differential signals first, lets talk about advantages and disadvanteges of rs 422485. Th e integrated optical diagnostics allow permanent monitoring of the fo paths during in. But since its dc levels i am reckoning it will be in the range of 6v and 0v. When you must have responses from slave devices, use a 4wire enhanced multidrop bus b. Reliable data communications can be difficult in the presence of induced noise, ground level differences, impedance mismatches, failure to effectively bias for idle line conditions, and other hazards associated with installation of a network. Multipoint rs485rs422 transceiversrepeaters check for samples. The idn com4 and rs422ars422b com4 and com5 ports are functionally equivalent, and default to rs422 mode in order to drive micros idn printers. The types of driver ics used in serial ports can be divided into three general categories. The icusb422 6ft professional rs422485 usb serial cable adapter with com port retention lets you connect rs422 or rs485 serial devices to your usbenabled computer. The pos application can convert this port to a simple two wire rs232 interface for driving serial peripherals. An example of a pullup and a pulldown resistor on an rs485 bus to ensure the proper voltages on an inactive bus. The lowpower, highspeed transceivers of this family are designed for rs485, rs422 and rs423 communication applications. Usb serial adapter usb to rs422 usb to rs485 9 pin.
The texas instruments sn65hvd37 ic used in this example includes a 3state enable input to force the two driver outputs into a highimpedance state. Ds26lv31t 3v enhanced cmos quad differential line driver. A builtin data direction autoturnaround feature automatically enables the rs485rs422 driver when data is present. The icusb422 6ft professional rs422 485 usb serial cable adapter with com port retention lets you connect rs422 or rs485 serial devices to your usbenabled computer. The circuit for ttlto rs422 converter is very simple. Usb serial adapter usb to rs422 usb to rs485 9 pin db9. This section summarises the key features of the ft232rq which apply to the usbrs422pcb. The connections for two devices with receive and transmit rs422 signals is shown in figure 1. 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. The output buffers of a cmos device may be cmos type or nmos type.
Dec 22, 2010 when a drivers output impedance is not matched to the transmission line characteristic impedance zo, there are reflections which causes ringing at the receiver as shown by the red waveform in the figure on the left. Rs485 summary of key specifications parameter conditions min max units driver output voltage, open circuit 1. Measuring input impedance and calculating output impedance. The output is differential mode driving, so it has two wires for each driver. February 2009 rev 16 119 19 st485b st485c low power rs485rs422 transceiver features low quiescent current. The max3040max3045 is a family of 5v quad rs 485rs422 transmitters designed for digital data transmission over twistedpair balanced lines.
The adapter features a 9pin db9 male serial connector as well as dipswitch controls for easy port configuration, and requires minimal software. Cable termination techniques, use of multiple loads, daisychaining of rs232, conversion of rs232 to rs485, conversion of rs485 to rs232, and rs232 portpowered rs485 conversions are described. The circuit for ttltors422 converter is very simple. Termination should be placed at the end of the network for each wire pair. The converter allows for 300 115200 bps transmission speeds. Guide to selecting and using rs232, rs422, and rs485.
Rs422 line driver to ni digital input termination ni. Therefore, cabling with impedance of 100w to 120w is recommended. For a basic rs 422485 system, we need an io driver with differential outputs and an io receiver with differential inputs. Rs422, specifications and in depth tutorial lammert bies. The icusb2324852 2 port usb to rs232 rs422 rs485 serial adapter with com retention lets you connect every type of serial device to your usbenabled computer, whether it be for rs232, rs422, or rs485 communication. I am purchasing an incremental encoder that has an rs422 line driver ouput. The receiver also includes an enable signal equipment manufacturers could use to turn off the receiver. Universal differential inputs accept lvds, lvpecl, necl, pecl, rs422 or ttl inputs differential 124. To enable the differential driver to be used, the rs422 standard uses a four conductor cable. Therefore, the cmos source impedance adds to the resistance of the resistor i believe. This converter will also repeat rs485 or rs422 with optoisolation. Mc26ls30 dual differential eia422a quad singleended. The rated output impedance is the impedance into which the amplifier can deliver its maximum amount of power without failing. Highlevel output current driver ioh 60 ma highlevel digital output current receiver.
The left hand is ttl level while the right hand is rs422 level. The effective impedance of the rmc serials termination resistor and biasing resistors is 114w. However, i can not find much information on the electrical characteristics of the 9411. Downloadable drivers, datasheets and utilities for all our products. Most rs422 devices show the output stage schematics in the data sheets.
Ten receivers can be connected to any one driver for use in multidrop systems. Rs422 will support pointtopoint, and multidrop circuits, but not multipoint. 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. A simple 2wire rs422 network a includes only one driver and as many as ten receivers. Snls072c may 1998 revised april 20 multipoint rs485rs422 transceiversrepeaters check for samples. The usbrs422 cable is a usb to rs422 levels serial uart converter cable incorporating ftdis ft232rq usb to serial uart interface ic device which handles all the usb signalling and protocols. The eia describes rs422 as a dte to dce interface for pointtopoint connections. An rs422 driver may have this signal, but it is not always required. Dec 29, 2014 i am trying to match a 50 ohm coax cable impedance with a series impedance at the driver. Rs422, also known as tiaeia422, is a technical standard originated by the electronic industries alliance that specifies electrical characteristics of a digital signaling circuit.
View more information about our rs485rs422 transceivers by category. When installing an rs422 device in a rs485 bus network should also be noted that a rs422 device rs485 bus network so heavily loaded as 3 rs485 devices, ie the maximum number of devices per station decreases. Optocouplers and optoisolators can be used on their own, or to switch a range of other larger electronic devices such as transistors and triacs providing the required electrical isolation between a lower voltage control signal, for example one from an arduino or microcontroller, and a much higher voltage or mains current output signal. Rs422 interface ic are available at mouser electronics. Rs232, rs485, rs422 drivers transmitters farnell uk. The rs485 specification specifies the capability to sustain up to 32 uls. The con485422rep is an effective solution for protecting rs232, rs485 and rs422 devices from voltage surges, lightning strikes, ground loop conditions and signal noise problems. Furthermore, where the rs232 line driver is only designed to serve one receiver, a rs422 line driver can serve up to ten receivers in parallel. How to properly configure and wire rs422 and rs485. Depending on the device receiver type, up to 32 12k impedance nodes or 11 rs422 receivers can be connected without a repeater. Low power rs485rs422 transceiver stmicroelectronics. The disconnected or disabled condition of the line driver usually is referred to as the tristate1 condition of the driver.
Ds26lv31t 3v enhanced cmos quad differential line driver check for samples. Only one device can transmit at a time, which is called a halfduplex operation. Bus drivers in slave devices must have the capability to switch their outputs into a high. Universal differential receiver, rs422 outputs pulse. Need a discrete configurable rs422 driver io board for pc. I was looking at the differential output driver of a rs422 transceiver with my scope, i had one output connect to the scope probe and the other connected to the scope probe ground. Rs422 differential driver maximum differential output. Differential lvds, rs422, lvpecl, necl, pecl or ttl to rs422 logic level translation differential line driverreceiver essential lab tools for interfacing with high speed data communications equipment features.
An rs232 port can supply only limited power to another device. A, each driver has a slew rate control pin which permits setting the slew rate of the output signal so as to comply with eia. Three common serial data standards, rs232, rs422, and rs485, are described by specification and electrical interface. The driver or generator is labeled d, the receiver is labeled r, and the termination impedance is zt. The actual output impedance for most devices is not the same as the rated output impedance. These monolithic quadruple differential line drivers with 3state outputs are designed to meet the requirements of ansi standards eiatia422b and rs485 and itu recommendation v.
The usbrs422pcb is a usb to rs422 level serial uart converter pcb incorporating ftdis ft232rq. What software commands set this cards output to a static output or reads the input high or low. Selecting and using rs232, rs422, and rs485 serial data. The input impedance of the rs485 receiver is specified as larger than or equal to 12 k this impedance is defined as having one unit load ul. Ftdi usb driver, the d2xx driver, can also be used with application software to directly access the. We use a load resistance r load, to load the signal source impedance z source. Now, we have a termination resistor of about 100ohms or 120ohms. Psi mos rs422fo data sheet 1description psi mos rs422fo devices convert rs422rs485 4wire and interbus interfaces to fiber optics. Output enable time to high level tpzh 31 65 ns rl 54. Il422 isolated rs422rs485 interface product datasheet. The serialcomm rep4854229e is an industrial grade bidirectional externally powered 2.
The termination resistor should match the characteristic impedance of the cable being terminated. As rs485 meets all the rs422 specifications table 3, rs485 drivers can be used in rs422 applications. Multithreaded tty is an easy to use high performance rs232 serial terminal program. This represents the rs422 connections of a device, card or converter. 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. This connection is commonly used for securitysurveillance video cameras to control the pantiltzoom available from pelco or others, or to connect displays for signage indoors or outdoors, clock displays, etc.
The slave devices cannot communicate with the driving device. Each device turns on its line driver only when transmitting data, and keeps it off in high impedance state for the remaining time to allow other devices to transmit. Combined impedance of a driver output and open collector pin with an internal 10 k. To connect a rs422 differential output to a ttl singleended input, in most cases it is sufficient to connect just one of the differential lines to the input and provide common ground of the input device and the encoder. Need a discrete configurable rs422 driver io board for.
Rs422 interface rs422 pin diagram rf wireless world. The receiver also includes an enable signal equipment manufacturers could use to turn. Line drivers and receivers are commonly used to exchange data between two or more points nodes on a network. To illustrate their basic differences, a condensed description of each standard is presented in the following subsections. Reliable data communications can be difficult in the presence of induced noise, ground level differences, impedance mismatches, failure to effectively bias for idle line conditions, and other hazards associated. 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. They usually contain one driver and one receiver in half duplex configuration. Analog devices offers a wide range of standard rs485. Oct 22, 2008 what software commands set this cards output to a static output or reads the input high or low. Additionally the rs422 standard allows for line impedances down to 50 ohms while supporting the high data rates. Rs422 driver can drive ten rs422 receivers in parallel. On the am26c31 for example, there is no diode drop to ground but there is a npn base emitter diode from vcc so maximum could be reduced to vcc. Emulates a com port or an ethernet device, that generates a serial stream of data.
This ability to compensate for manufacturing tolerances of some components enables test specifications to be relaxed and saves component and tester costs. When b a then the output is a mark 1 or off and when a b then it is counted as a space 0 or on. April 4, 2007 rs485 rs422 and rs232 cable information. Rs485 transceivers are available in both industrystandard packages and small, spacingsaving packages. Incremental output driver set the output driver to pushpull htl or rs422 ttl pulses per revolution program the ppr to a defined value. It was intended to replace the older rs232c standard with a standard that offered much higher speed, better immunity from noise, and longer cable lengths. Usb to rs422 uart serial converter pcb datasheet version 1. The conversion is performed using a transparent protocol for all data rates up to max. Drivers output impedance from ibis bert simonovichs.1116 432 1634 231 301 1173 565 1155 1025 628 112 940 1382 594 1369 703 513 212 744 1021 915 992 433 444 766 1414 563 706 1003 1435 249 146 55 1445 118 875 3