Going for distance or going for speed on the RS-485 bus?


Network designers know that for robust, reliable communications, the RS-485 standard has a track record that has made it the recommended standard for multipoint, differential data transmission in industrial networks. And although the RS-485 standard has stood the test of time, as other elements of the system or network change, RS-485 transceivers have evolved to meet those needs. Modern networks are often a combination of control systems and data links with requirements that vary by application. 

As more demands are placed on networks, many equipment makers require control channels to span longer distance in the network as well as send high-speed data through the network. The RS-485 bus standard supports data transmission as far as 4000 ft (1200 m), but at the maximum cable length, the maximum data rate is not obtainable: the longer the cable, the slower the data rate.

That’s where selectable data rate comes in to save the day for applications requiring synchronous (parallel transceiver) signal timing. You no longer have to decide between cable length and data rate. By qualifying the new SN65HVD01 selectable data-rate transceiver once, designers can find common ground between going the distance and going for speed. A programmable logic controller (PLC) designer can use the SN65HVD01 transceiver to send control information up to 250kbps to remote IO modules that are across the factory up to 1200 m from the PLC. Some industrial networks may require larger amounts of data to move between nodes in the network; and by using the slew-rate select feature, the same device can support much higher data rates up to 20Mbps.

 

Driving down power consumption in these networks is becoming more critical as well. Very low standby current that can interface to either a 3.3V or 1.8V FPGA or microprocessor, helps to achieve lower system power as well as reduces costly level translators. 

Upgrading is easy too.  Modern transceivers are designed for backward compatibility to basic RS-485 transceivers, but can give you the benefits of more flexibility and robustness. SN65HVD01 is one of many devices in the RS-485 transceiver portfolio to support IEC ESD protection - now that’s flexibility without a tradeoff!  If this transceiver were a vehicle on the RS-485 bus, think of it as the fast sports car with hybrid power consumption and tank-like protection that will go the distance if you need it to. 

What’s bogging down your RS-485 system? Would selectable data rate help your design?

To keep your isolation on track in any industrial system, check out TI’s ISO7131cc device, especially those looking to reduce board space.

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