Fecha 07.04.2018

Autor Deltaiytqay

Asunto Ошибка на частотнике экструдера

of R.E. Smith . RS-485 transceiver, or other component. The primary node’s serial port connects to a series of RS-485 transceivers. Each transceiver in turn connects via RS-485 to one or more nodes in the network. When the primary node transmits, the data passes through all of the transceivers to the secondary nodes. When a secondary node transmits, a transceiver passes the data to the primary node but not to the other secondary nodes. When all of the transceivers’ R outputs are logic highs, a 4.7k resistor holds the primary node’s input high. When a transceiver’s R output goes low, the primary node’s input goes low. All of the transceivers derive their driver-enable signals from the data as described in Chapter 6. Using this method to control the driver-enable signals greatly simplifies the network programming for the circuit. 143 This page intentionally left blank 8 Going Wireless Communicating without wires has great appeal. Wireless data can pass through walls and travel for miles. Portable devices are easier to use when there are no data cables to attach and route. Plus, wireless communicating is fun. Even in an age when wireless phones and networks are routine, there’s something entertaining about designing a system that sends and receives information with no visible connection between the sender and receiver. A data-communication system must carry information to the receiver at the desired speed, without errors, and without causing interference to other electronic devices. For many applications, wired interfaces meet these requirements easily and at low cost. Where cables aren’t possible or desirable, wireless technologies are an alternative. This chapter presents options for selecting and implementing wireless technologies for transferring asynchronous data. 145 Chapter 8 Media and Modulation Designing a wireless communication system requires deciding on a transmission medium, a modulation method if needed, and a protocol for transferring data