The amplitude of the carrier signal varies depending on the binary stream of incoming data. ASK is sometimes still used for low data rates, but it has difficulty distinguishing the signal from the noise, because noise in the communication channel is an amplitude-based phenomenon. The start, stop, and parity bits used in asynchronous transmission systems are normally physically generated by a standard IC chip (integrated circuit) that is part of the interface circuit between the microprocessor bus and the line driver (or receiver) of the communication connection. This type of IC is called UART (Universal Asynchronous Receiver/Transmitter) or sometimes ACE (Asynchronous Communications Element). The CRL contains the description of all communication relationships of a device, regardless of when it is used. Chapter 3: Serial Communication Standards. This chapter presents the main physical interface standards related to data communication for instrumentation and control systems. ITU defines a full range of standards for the connection of telecommunications equipment. Standards for data reporting devices are generally defined by the ITU-T “V” series recommendations. Therefore, the sample of bits observed on the communication connection is as follows, with each bit being read in order from right to left. Modbus Plus Bridge/Multiplexer is a practical example of the alternative use of a multiplex in TDM mode.
This makes it possible to connect Modbus-based devices to Modbus Plus networks. The example illustrates the use of a multiplexer in the broad sense rather than maximizing the use of a communication channel. Figure 7.29 shows AEG Modicon`s NW-BM85-000 Modbus Plus Bridge/Multiplexer. Note that the asynchronous connection can use either a full-duplex (unpolished) protocol or master-slave communication via a half-duplex (unpolished) protocol. Although both types of protocols are available, the trend today is to use the full duplex protocol, as this explains the high performance of the connection. That is why this protocol will be examined more closely in the following sections. . . .