Card Setup

RS-485 Enable Modes

RS-485 is ideal for multi-drop or network environments. RS-485 requires a tri-state driver (not dual-state) that will allow the electrical presence of the driver to be removed from the line. The driver is in a tri-state or high impedance condition when this occurs. Only one driver may be active at a time and the other driver(s) must be tri-stated. The output modem control signal Request To Send (RTS) is typically used to control the state of the driver. Some communication software packages refer to RS-485 as RTS enable or RTS block mode transfer.

One of the unique features of the OMG-ULTRA-COMM422is the ability to be RS-485 compatible without the need for special software or drivers. This ability is especially useful in Windows, Windows NT, and OS/2 environments where the lower level I/O control is abstracted from the application program. This ability means that the user can effectively use the OMG-ULTRA-COMM422in an RS- 485 application with existing (i.e. standard RS-232) software drivers.

Headers J1D through J4D are used to control the RS-485 mode functions for the driver circuit. The selections are ‘RTS’ enable (silk-screen ‘RT’) or ‘Auto’ enable (silk-screen ‘AT’). The ‘Auto’ enable feature automatically enables/disables the RS-485 interface. The ‘RTS’ mode uses the ‘RTS’ modem control signal to enable the RS-485 interface and provides backward compatibility with existing software products.

Position 3 (silk-screen ‘NE’) of J1D through J4D is used to control the RS-485 enable/disable functions for the receiver circuit and determine the state of the RS-422/485 driver. The RS-485 ‘Echo’ is the result of connecting the receiver inputs to the transmitter outputs. Every time a character is transmitted, it is also received. This can be beneficial if the software can handle echoing (i.e. using received characters to throttle the transmitter) or it can confuse the system if the software does not. To select the ‘No Echo’ mode select silk-screen position ‘NE’.

For RS-422/530/449 compatibility remove the jumpers at J1D through J4D.

Examples on the following pages describe all of the valid settings for J1D - J4D.

OMG-ULTRA-COMM422

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Omega Engineering RS-422/485 manual RS-485 Enable Modes
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RS-422/485 specifications

Omega Engineering is a renowned leader in the field of measurement and control technologies, particularly in the realm of data communication for industrial automation. The RS-422 and RS-485 protocols are part of Omega's robust offering, designed to facilitate reliable and efficient data transmission over relatively long distances. These protocols are widely used in various applications ranging from industrial machinery to building automation systems.

One of the main features of RS-422 is its ability to support long-distance communication, allowing data to be transmitted up to 4,000 feet (approximately 1,200 meters) at speeds of up to 10 Mbps. This is achieved through the use of differential signaling, which provides improved noise immunity compared to single-ended signaling systems. RS-422 employs a single transmitter and multiple receivers, making it ideal for point-to-multipoint configurations.

On the other hand, RS-485 extends the capabilities of RS-422 by allowing multiple devices to be connected on the same bus. It supports up to 32 devices, which can be either transmitters or receivers, making it exceptionally versatile for networking applications. RS-485 can communicate effectively over distances up to 4,000 feet and at speeds of 10 Mbps as well. This makes it an attractive option for applications where several devices need to communicate with a central controller.

An essential characteristic of both protocols is their resilience to electromagnetic interference, which is often a concern in industrial environments. The differential signaling used in RS-422 and RS-485 reduces noise susceptibility, ensuring data integrity even in challenging conditions. Additionally, these protocols function effectively in half-duplex or full-duplex modes, providing flexibility based on application requirements.

Moreover, Omega Engineering’s implementations of RS-422 and RS-485 comply with established standards, ensuring compatibility with a wide range of devices. This interoperability is crucial for seamless integration into existing systems and enhancing overall productivity.

In summary, Omega Engineering's RS-422 and RS-485 technologies offer robust, reliable, and versatile solutions for data communication in industrial settings. With features such as long-distance communication, multiple device connections, and exceptional noise immunity, these protocols continue to serve as foundational technologies in various automation and control applications. As industries evolve, Omega Engineering remains committed to advancing these technologies to meet the growing demands of modern data communication.
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