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If the clock idles in the high state, the leading edge of the clock is a falling edge. If the total Unit Load is too high, the voltage drop across all devices will be too significant, leading to signal degradation. The signal is a voltage change across a load as low as 1.5 volts differential from a driver, with a receiver detecting a differential voltage as minute as 200 millivolts. The most common cable type is Cat 5e-UTP (unshielded twisted pair) which may work over shorter distances in less demanding applications with low EMI noise levels. If your computer does not have an RS-232 serial port, low cost USB-to-RS-232 serial cables are available; contact Mosaic Industries for details. The advantage of such a multi-drop RS-232 network is that the communications are full duplex, with each communicating party capable of simultaneous transmission and reception of data. On the other hand, RS485 is more industry-based communication which is developed for a network of multiple devices that can be used over long distances and at greater speeds too. A Modbus RS485 connects a Master device to one or more Slave devices. The cable shield must be earthed only in one point. Note that this Hackster project does something similar with splicing an ethernet cable to a UART breakout module.

The device ships with an Ethernet RS-485 communication interface as well as a RS-485 to USB cable, which is said to be able to communicate with a PC using proprietary Windows based software (and driver, I think). No I have not been able to test this using the Windows software. To make sure that your USB to RS-485 cable & the device RS-485 port are working, have you tried using them with a Windows PC and the manufacturer's s/w? Each device has a communication port with two terminals, which are indicated for the sake of convenience as A and B. In these two terminals the communication cable is connected so that all the devices that take part in the communication are connected in parallel. While the default baud rate of the primary serial port is 9600 baud, you can speed your communications and download times appreciably by switching to a faster baud rate. It operates at a maximum data rate of 10 Mbps and can transmit data over long distances of up to 1200 meters. Maximum length is 4000 ft.

The maximum number of devices that can be connected to a main cable is 32, including the Master. The end resistance must be used only at the ends of the main cable. End of line termination resistor (120 ohm 1/4 watt) to be installed at both ends of network. A simple network of a PLC, VFD, and an HMI allows remote control of motors in an industrial setting. The RS485 standard allows the user to configure inexpensive local networks and multidrop communications links using twisted pair wire. This allows you to configure full duplex multi-drop networks in which a single master can sequentially address one of many slaves and start a full-duplex exchange of data. One transmitter and 10 receivers are allowed on a network, with a distance limit of 3600ft. RS422 was on the market prior to RS485; however, due to loading limitations, one of the best uses of RS422 is probably in point-to-point communications, such as RS232 extension cords. In practice, Cat 5 cables have been used successfully in many installations, but there are some concerns. For example, at 4800 baud (bits per second), each bit lasts about 200 microseconds (µs), and if communications are full duplex (e.g., if the QScreen Controller echoes each incoming character), then there is a serial interrupt every 100 µs or so.

The capacitance is close to 12.5 pF/foot but there is a small impedance mismatch (100 ohms for Cat 5, 120 ohms for RS-485). 100 ohms, Cat 5 cables almost meets the electrical requirements for RS-485 cables. These detailed signal descriptions and cable diagrams are presented to provide complete information for those who have special communications requirements and for those who wish to make their own application-specific communications cables. In general, all devices on a network should use the same phase, polarity, and baud rate clock signal. To properly operate the network each slave computer executes RS232Silent at startup; thus all of the slave transmitters remain silent individually addressed by the master. The DMX standard is very strict: Each pair is unidirectional (like RS422), it uses longer mark and space times between datablocks than specified in computer Serial communication. The branches must be no longer than 1200 m! Longer branches could cause signal reflections and generate disturbances and consequent errors in the reception of data. The main cable must be no longer than 700 m! Using a repeater, the main cable is divided into different segments, each of which can be up to 700 m in length and connect 32 devices (this number includes the repeaters).

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