Bus (Bus) is a variety of computer functional components to transmit information between the public **** communication trunk, it is composed of wires transmission harness, in accordance with the type of information transmitted by the computer, the computer's bus can be divided into data bus, address bus and control bus, respectively, for the transmission of data, data address and control signals. Bus is an internal structure, it is the cpu, memory, input and output devices to transfer information common channel, the host of the various components connected through the bus, external devices through the corresponding interface circuit and then connected to the bus, thus forming a computer hardware system. In the computer system, between the various components of the information transfer between the public **** path called bus, microcomputer is a bus structure to connect the various functional components. When the bus is idle (other devices are connected to the bus in a highly resistive state) and a device wants to communicate with the destination device, the device initiating the communication drives the bus and sends out the address and data. The other devices connected to the bus in a highly resistive state receive the data on the bus if they receive (or can receive) address information that matches their own. The transmitting device completes the communication and lets the bus out (the output changes to a high resistance state). nbsp; nbsp; nbsp; Bus according to the function and specification can be divided into three major types: (1) Chip Bus (Chip Bus, C-Bus) three types of bus in the microcomputer system status and relationship, also known as the component level bus, is a variety of different chips are connected together to form a specific function module (such as CPU module) of the information transmission path. (2) Internal Bus (Internal Bus, I-Bus), also known as the system bus or board level bus, is a microcomputer system between the plug-in (module) information transfer path. For example, the transmission path between the CPU module and the memory module or I/O interface module. (3) External Bus (External Bus, E-Bus), also known as the communication bus, is a microcomputer system or microcomputer system and other systems (instruments, meters, control devices, etc.) between the information transfer path, such as EIA RS-232C, IEEE-488, etc.. One of the system bus, that is, in the usual sense of the word bus, generally contains three different functions of the bus, namely, the data bus DB (Data Bus), address bus AB (Address Bus) and control bus CB (Control Bus).