Examples of data rate and cable length combinations vary from 90 kbps at 4000 feet to 10 Mbps at 15 feet for RS-422. Maximum Cable Length 50 FT. Maximum Recommended Data Rate: In 1998, when the standard was introduced, the maximum recommended data rate was 10Mbps, and it could be achieved with a cable length of 12 meters or 40 feet. The most important thing to keep in mind when choosing a USB RS485 converter or USB RS422 adapter is if you need a standard or industrial strength USB to RS485 converter or USB to RS422 adapter and whether it needs to be isolated or non-isolated. However since only a true RS485 network can have addressable serial RS485 devices, the RS232 converter needs to be addressable either by software or by DIP switches when using it in this type of configuration. USB to RS485 is known for its multi-drop characteristics, meaning you can use USB RS485 for connecting multiple RS485 devices in a two-wire network.

Some of these converter / adapter units can convert only USB to RS485 or USB to RS422 but others can convert both RS485 and RS422 at the same time. The isolated USB to RS485 converter / USB to RS422 adapter is used in many industrial and business environments since these are resistant to moderate voltage spikes and noise levels. Receiver Input Resistance (Ohms), (1 Standard Load for RS485) 3k to 7k 4k min. The reason we call it a standard converter is that it is considered a converter with a minimum of the general features and requirements for converting a RS232 signal to a RS485 signal and a RS485 signal to a RS232 signal. Why use a RS232 - RS485 /RS422 converter? Network topology is probably the reason why RS485 is now the favorite of the four mentioned interfaces in data acquisition and control applications. The typical RS232 to RS485 converter comes in many different shapes and sizes. Most newer consumer electronics comes with an USB, Firewire or other high-speed communication port, however a lot of industrial and commercial equipment, both old and new, is made only with a RS485 or RS422 serial communications port. RS485 is used in many computer and automation systems.

You can think of RS485 as a "party-lined" communications system (the addressing is handled by the Remote Computer unit). Since most computers do not have a RS485 or RS422 port, but they do have a USB port, you can use a USB to RS485 converter or USB to RS422 adapter to interface between your computer and your device. Obligatory indicator LED (D406, R405) for showing that USB is connected. The standard USB RS485 converter / USB to RS422 adapter is a non-isolated adapter which is used for many business, office and personal devices. Even RS485 is not commonly as popular as RS232 it is extremely useful for converters in industrial and commercial environments. The RS422 converter is used for data transmission, using balanced or differential signaling, it is mainly used in industrial and commercial environments since lots of process equipment and machinery have this protocol built-in. USB to RS422 is often used for extending a RS232 wire by using a USB to RS422 adapter at each end of a RS232 wire. I've add some length/skew compensation although frankly with USB Full Speed it's hardly required4.

Choosing the correct USB RS485 converter or USB RS422 adapter is often a fairly easy task since most converters / adapters work within a range of multiple settings. The USB to RS485 converter and USB RS422 adapter, also called USB to RS485 / USB RS422 converters, are small electronic devices used for converting a USB signal into either RS485 or RS422. The USB-RS485 module uses the FTDI FT232R USB chip to handle all the USB protocols. The RS485 converter interface uses two wires for communication, one for transmitting and one for receiving data, which is referred to as a half-duplex communication converter. Due to loading limitations one of the best uses of a RS232 to RS422 serial converter might be in point-to-point communications, such as extending an existing RS232 line. The control board and feeders aren't very far apart so noise might not be a big enough issue on untwisted cables in practice. If there is a lot of environmental electrical noise then an optical isolated converter is preferred. There are several factors to consider when choosing a RS232 - RS422 converter. Because of this, the resulting noise current is many factors lower than with an ordinary straight cable.

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