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In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. Many characteristics of the transmitters and receivers are the same as RS422. Circuit grounding is not shown in either of the RS422 or RS485 circuits. It has an RS485 digital communication interface for setup of transducer parameters and to provide real time pressure measurement. The 974B-72034 QuadMag Cold Cathode / MicroPirani / Piezo Transducer offers a measurement range from 1x10-8 to 1500 Torr and features a 2.75 inch CF flange fitting. RS-485 signals are used in a wide range of computer and automation systems. If a star configuration is unavoidable, special RS-485 repeaters are available which bidirectionally listen for data on each span and then retransmit the data onto all other spans. RS-485 only specifies the electrical characteristics of the generator and the receiver: the physical layer. It also defines three generator interface points (signal lines); A, B and C. The data is transmitted on A and B. C is a ground reference. Section 4 defines the electrical characteristics of the generator (transmitter or driver), receiver, transceiver, and system. Normally required once the system has reached it's quiescent state, when no drivers are driving the bus.

RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. Such installations are not standard, but they do work. These manufacturers all agree on the meaning of the standard, and their practice is in widespread use. To be on the conservative side, it is always best to use dual twisted pair shielded transmission cable for RS485. RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422. The EIA has officially disbanded and the standard is now maintained by the TIA as TIA-485, but engineers and applications guides continue to use the RS-485 designation. 100 Mbps over standard Ethernet physical layers. It does not specify or recommend any communications protocol; Other standards define the protocols for communication over an RS-485 link. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Under some conditions it can be used up to data transmission speeds of 64 Mbit/s. As a rule of thumb, the speed in bit/s multiplied by the length in metres should not exceed 108. Thus a 50-meter cable should not signal faster than 2 Mbit/s.

No maximum bus length is given for RS485, but ends up around 1200 meters at 200kbps or 50 meters at 10Mbps. The speed of the system and distance between devices is determined in large amount by the inter-connecting cable. Repeaters may be used to extend the net to any number of devices. It may be used to control video surveillance systems or to interconnect security control panels and devices such as access control card readers. The equipment located along a set of RS-485 wires are interchangeably called nodes, stations or devices. Its main hardware functions are address decoding, baud rate generation, parallel-to-serial and serial-to-parallel conversion, input/output port selection, input port buffering and output port latching. If you would rather skip the detail, please do not hesitate to jump ahead to the section, BAUD RATE SETTINGS. The foreword to the standard references The Telecommunications Systems Bulletin TSB-89 which contains application guidelines, including data signaling rate vs. The standard is jointly published by the Telecommunications Industry Association and Electronic Industries Alliance (TIA/EIA).

The Series 970B have standard 15 pin HD Sub-D connector. RS-485 I/O (N,O) - These are standard RJ-15 4 pin modular connectors for connection to a multidrop network. Looking at RC5, Pin 24, the Transmit Enable (TXEN) line, this is a little more complicated. This is extremely heavy filtering and probably more than needed for even the most severe situations. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone. The driver IC on the RS485 card is capable of driving 32 unit loads or 128 of the ¼ load devices. Many (on-line) App-notes use 12K ohms as an input impedance, 60 ohms (as a termination), 3.5 mA as the minimum 'load' current, RS485 standard and 10 loads. Ideally, the two ends of the cable will have a termination resistor connected across the two wires. The value of each termination resistor should be equal to the cable characteristic impedance (typically, 120 ohms for twisted pairs). Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. RS-485 and RS-422 can interoperate with certain restrictions.