This FTDI converter cable provides a fast, simple way to connect devices with an RS485 interface to USB. The RS485 system used for Modbus communication provides a main cable (Bus or backbone), to which all the devices have to be connected with branches (also known as stubs) that are as short as possible. Default, all the senders on the RS485 bus are in tri-state with high impedance. RS485 drivers automatically return to their high impedance tri-state within a few microseconds after the data has been sent. Because of this RS485 and the others can be used in situations with a severe ground level shift of several volts, where at the same time high bit rates are possible because the transition between logical 0 and logical 1 is only a few hundred millivolts. In most higher level protocols, one of the nodes is defined as a master which sends queries or commands over the RS485 bus. N nodes are connected in a multipoint RS485 network. RS485 is the only of the interfaces capable of internetworking multiple transmitters and receivers in the same network. RS232 has a separate communication line for transmitting and receiving which-with a well written protocol-allows higher effective data rates at the same bit rate than the other interfaces.

This robustness is the main reason why RS-485 is well suited for long-distance networking in noisy environment. It is the reason why RS485 is so popular with computers, PLCs, micro controllers and intelligent sensors in scientific and technical applications. Network topology is probably the reason why RS485 is now the favorite of the four mentioned interfaces in data acquisition and control applications. When using the default RS485 receivers with an input resistance of 12 kΩ it is possible to connect 32 devices to the network. TSB-89A, Application Guidelines for TIA/EIA-485-A does not recommend using star topology. Although total cable length maybe shorter in a star configuration, adequate termination is not possible anymore and signal quality may degrade significantly. The RS485 network must be designed as one line with multiple drops, not as a star. In multifunction instruments, not only the cables connected to the measurement, but also the RS485 serial port and the analog and digital inputs and outputs must be wired. The end resistance must be used only at the ends of the main cable.

Use 100 Ω resistors on both ends. For higher speeds and longer lines, the termination resistances are necessary on both ends of the line to eliminate reflections. The USB-16COMi-RM serial adapter is an isolated serial port COM adaptor for RS 42-232/485. Even in extremely heavy systems, a high-speed serial port capable of supporting 128 byte FIFO can be used to communicate with one another at high speeds. The 1-port USB to Serial Com port can connect to a USB 2.0 port and can be configured to use RS-485 peripherals such as POS devices and industrial control devices. On the other side we also have converter RS232 - RS485 ATC - 108N, via the RS232 port is connected to cash or other device with RS232 port. And that with an interface which does not require intelligent network hardware: the implementation on the software side is not much more difficult than with RS232. With such an implementation of a RS485 network it is necessary that there is error detection implemented in the higher level protocol to detect the data corruption and resend the information at a later time.

The RS485 chip converts CMOS level transmit (Tx) and receive (Rx) lines to differential RS485 voltages than can be sent over long distances. Depending of the information in the sent data, zero or more nodes on the line respond to the master. 5. Scalability - RS485 can be easily scaled to support more devices or higher data throughput as needed.6. Educators and students working in laboratories and classrooms in universities across the country often use older paper chart recorder technology to record their live data onto hard copy. If you want to connect a device with an RS485 interface to a computer via USB, you’ll need to use a USB to RS485 cable. FTDI USB to RS485 Serial UART Converter Cable incorporates FTDI's FT232RQ USB to serial UART interface IC, which handles all the USB signaling and protocols. Each FTDI USB-RS485 cable contains a small internal electronic circuit board utilizing the FT232R that is encapsulated into the USB connector end of the cable. Most manufacturers still utilize a DB-9 connector. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone. This would enable the same standards to be used worldwide and also give manufacturers access to a global market using just one product.