Electronics Industries Association

high and vice-versa. Also, the drivers are capable of driving a wire with as much as 25 times more capacitance before the signal is badly distorted. Most system designers try to minimize the number of signals used because these standards take two wires per signal. This is one reason most RS-422 and RS-485 systems are either two-wire with ground or four-wire with ground.

There are two major differences between RS-422 and RS-485. The first is that with RS-422, one driver can only drive 10 receivers. With RS-485, one driver can drive 32 receivers. Secondly, RS-485 drivers can be “tri-stated” or turned off. This allows you to put all 32 drivers and receivers on one two-wire line. When a device needs to output data, it first turns on its driver to seize the line and then sends its data. The other 31 devices will be listening. RS-422 requires at least two pairs of wires, one pair to send data in one direction and the other for return data.

Typically, the RS-422 or RS-485 driver will switch between +5 volts and ground. Since devices can be long distances apart, they can be powered on different power lines or transformers that can force their “reference grounds” to be at different voltages. The RS- 422 Standard allows the signal lines to go as high as +7 volts and as low as -7 volts. The RS-485 Standard allows +12 volts and -7 volts.

Another requirement is that the differential input voltage at the receiver must be more than 0.2 volts. The differential voltage starts out from the driver at about 2 volts but the resistance, inductance, and capacitance of the wire combine to attenuate this signal. As the wire gets longer, this voltage will get smaller until it falls below the

0.2volt level and then communications can no longer be guaranteed.

Both specifications discuss termination of the two-wire line. A typical two-wire twisted-pair line looks like a 100 ohm transmission line. In general, the line does not need to be terminated for slow data rates or for short-wire lengths.

More information and the RS-232, RS-422, and RS-485 Standards are available from:

Engineering Department

2001 Eye Street N. W.

Washington, DC 20006

Phone: (202) 457-4900 --- FAX: (202) 457-4985

2Documentation Number 485T1995 Manual

B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

PH (815) 433-5100 -- FAX (815) 433-5105

485T specifications

B&B Electronics has been a prominent player in the field of industrial connectivity solutions, and one of their notable products is the 485T. The 485T is a robust serial communication device designed specifically for converting RS-232 signals to RS-485. This device is particularly valuable in environments that necessitate reliable signal transmission over extended distances, which is where traditional RS-232 connections typically fall short.

One of the standout features of the B&B Electronics 485T is its ability to support communication over long distances of up to 4,000 feet. This makes it an ideal solution for applications in industrial settings, where distances between devices often exceed the limitations of standard serial connections. With data rates of up to 115.2 kbps, the 485T ensures that information can be transmitted swiftly and efficiently, making it suitable for various real-time monitoring and control applications.

The 485T incorporates advanced technologies that enhance its performance and reliability. For instance, it features built-in surge protection, which safeguards the device and connected equipment from voltage spikes and transient events. This is crucial in industrial environments where electrical noise and surges can be commonplace. Additionally, the device is designed to support multiple nodes on the RS-485 network, accommodating up to 32 devices simultaneously. This versatility allows for expanded networking capabilities, making it easier to integrate multiple devices and sensors into a cohesive communication system.

In terms of configuration, the B&B Electronics 485T is user-friendly, featuring jumper settings that allow for quick adjustments to accommodate different application requirements. Users can easily switch between half-duplex and full-duplex modes, providing greater flexibility based on the needs of their specific communication networks.

The 485T's compact design makes it easy to integrate into existing systems without taking up excessive space, and its durable construction ensures reliability in demanding environments. Furthermore, with a temperature range designed to withstand industrial conditions, the device can function effectively in both warm and cold settings.

In conclusion, the B&B Electronics 485T is a powerful solution for anyone in need of reliable and long-distance RS-232 to RS-485 conversion. With its high data rates, long-distance capabilities, and enhanced durability, the 485T serves as an excellent choice for industrial communication applications, ensuring that devices remain connected and operational even in the most challenging environments.