The concept and interface circuit of serial communication comes from China Industrial Control Network With the application of computer systems and the development of microcomputer networks, communication functions are increasingly important. The communication mentioned here is only the information exchange of the computer and the outside world. Therefore, communication includes both a computer and an external device, and includes information exchange between a computer and a computer. Since the serial communication is a transfer information of a transmission line, the transmission line used is small, and information is transmitted by means of the ready-made telephone network, and therefore, it is particularly suitable for remote transmission. It is also common for those who are not far from the computer-machine exchange device and serial storage of the computer such as terminals, printers, logic analyzers, disks, etc., using serial mode. In real-time control and management, in multiple microcomputer processor sets, communication between each CPU is generally a serial mode. So the serial interface is a commonly used interface for the microcomputer application system. Many peripherals and computers communicate in a serial manner, which is the serial way to refer to information transmission between peripherals and interface circuits. In fact, between CPUs and interfaces work in parallel. 1 Concept of Serial Communication Figure 1-1 Such "Serial Communication" refers to the use of a data signal line between peripherals and computers (in addition to the ground, may also need control lines), data on one data signal line One one is transmitted, and each data occupies a fixed time length. As shown in Figure 1-1. This communication method uses less data cable, which can save communication costs in long-distance communication, of course, its transmission speed is slower than in parallel. Since the CPU and the interface are transmitted, the interface and the peripheral are transmitted, and therefore, in the serial interface, there must be "Receive Displacement Register" (string → and) and "send displacement Register "(and → string). The structure of a typical serial interface is shown in 1-2. Figure 1-2 During the data input, 1 bit bit from the peripheral enters the "Receive Displacement Register" of the interface, and the data is from the "receiving shift register", the data is from "Receive Displacement Register" enters "Data Enter Register". The CPU reads the received character from the "Data Input Register". (Parallel read, that is, D7 ~ D0 is also read to the accumulator). The shift speed of the "Receive Shift Register" is determined by the "Receive Clock". During the data output, the CPU is sent to the "Data Output Register" and "Data Output Register" to "Transmit Shift Register" and then shift by "Send Displacement Register". , Send 1 bit of 1 bit to peripherals. The shift speed of the "Send Displacement Register" is determined by the "Send Clock". The "control register" in the interface is used to accommodate the various control information given to this interface, which determine the operating mode of the interface. The "Status Register" is called "status bit", each of which can be used to indicate status or certain errors during data transfer. For example, the D5 bit of the status register indicates "Data Output Register" empty, indicating "data input register full" with D0 bits, indicating "parity error", etc. with D2 bits. The above-described "String <-> and" conversion function can be completed, commonly referred to as "Universal Asynchronous Receiver and Transmitter," typical chips are: Intel 8250/8251, 16550.
