-
Basic Concepts of Buses
Bus connection: connect the five major components of the computer to a group of public information transmission lines in the greenhouse
Bus: An information transmission line connecting multiple components. It is a transmission medium shared by each component. In fact, it consists of many transmission lines or paths. Each transmission line can transmit binary code bit by bit.
Most modern computers use various bus structures
-
Classification of buses
According to the transmission mode: serial transmission bus, parallel transmission bus
According to the transmission data width: 8, 16, 32, 64 bits, etc.
According to the scope of use: computer bus, measurement and control bus, network communication bus
The bus is introduced according to the connected components:
-
On-chip bus
Refers to the internal bus of the chip, such as inside the CPU, connecting registers and registers, registers and ALU units
-
system bus
Refers to the information transmission line between the CPU, I/O devices, and main memory components.
Data bus: transmits data information between functional components, bidirectional transmission bus, the number of bits is related to the word length of the machine, and the length of the storage word, the number of bits of the data bus is called the width of the data bus, an important parameter to measure the system performance
Address bus: The address of the source data or destination data on the data bus is transmitted at the same time. The address information is unidirectionally output by the CPU. The number of bits of the address line is closely related to the number of storage units. Main memory with 20 address lines has 2^20 memory cells
Control bus: Both the data bus and the address bus are shared by the components hanging on it. The control signals transmitted on the control bus allow each component to have control over the bus at different times.
-
communication bus
For communication between computer systems and between computer systems and other systems. Transmission rate and transmission distance are inversely proportional. The rate of parallel transmission is much higher than that of serial transmission, but the cost of parallel transmission is very high, so in long-distance transmission, serial transmission is generally used.
-
Bus characteristics and performance indicators
Machine characteristics: the characteristics of the bus in the way of mechanical connection
Electrical characteristics: specify the transmission direction and effective level range of signals on each transmission line on the bus. It is worth noting that the level signal of RS-232C is inverse logic, that is, the low level is 1, and the high voltage is 0
Functional characteristics: specify the function of each transmission line, such as address line transmission address code
Time characteristic: refers to when the signal of the transmission line on the bus is valid
-
bus structure
Bus width: the number of bus transmission lines
Bus bandwidth: The number of bits or bytes of data transferred per second. eg. A bus with a working frequency of 100MHz and a line width of 32 bits has a bandwidth of: 100M*32/8B/1s = 400MBps (megabytes per second)
Clock Synchronous/Asynchronous: Whether the data transfer is synchronized with the clock signal
Bus multiplexing: Whether two kinds of signals are transmitted on one bus. Usually the address bus and the data bus are multiplexed, and at different times, the bus transmits different signals
Number of signal lines: the sum of the number of lines of the address bus, data bus, and control bus
Other indicators: such as load capacity, power supply voltage, etc. The load capacity of the bus is the driving capacity. When the bus is connected to the load, whether the output logic level of the bus can be maintained within the rated range
-
bus standard
The bus standard is an interconnected standard interface between the system and each module, and between modules. This interface is transparent to the modules at both ends, that is, either side of the interface only needs to complete their own interface function requirements according to the bus standard, without knowing the connection requirements between the other party's interface and the bus, so the interface designed by the bus standard can be regarded as a general purpose. interface
Several common bus standards
ISA bus: (industrial standard architecture) industry standard architecture bus, which uses a clock frequency independent of the CPU, so it can use a clock higher than the bus frequency, which is conducive to the improvement of CPU performance. There is no hardware logic that supports bus arbitration, so it does not support multiple A master device system, and all data transfers must be managed through the CPU or DMA interface, so the CPU spends a lot of time controlling the exchange of data with external devices. The operating frequency is 8MHz, the data line is 16 bits, and the address line is 24 bits
PCI: Due to bandwidth limitations, the ISA standard is not suitable for GUI and multimedia applications. (peripheral component interconnect) peripheral component interconnection.
High performance: It is not attached to the local bus of a specific processor, provides a high-speed data transmission channel for the system, adopts 33MHz or 66Mhz bus clock, and the data line is 32 bits, which can be extended to 64 bits. Support burst operation. This method means that if the transmitted data is stored continuously in the main memory, when accessing the data, only the first data address needs to be given, which takes one clock cycle, and then each data is transmitted. Each occupies one clock cycle, and it is not necessary to give each data address each time, thereby increasing the transmission rate
Good compatibility: bus components and plug-in interfaces are independent of the processor, support all current and future processors of different architectures, and have a relatively long life cycle
Plug and play support: any expansion card can work as long as it is plugged into the system
Support multi-device capability, provide data and address parity function, support two voltages, good scalability, and use multiplexing. . .
RS-232C: A serial communication bus standard recommended by the Electronic Industries Association (EIA) for serial binary exchange of data terminal equipment and data communication equipment.
USB bus: (universal serial bus) Universal serial bus, based on universal connection technology, realizes simple and fast connection of peripherals, achieves the purpose of user convenience, cost reduction, and expansion of PC peripherals. It has the characteristics of true plug and play, and I believe everyone has such a feeling in daily life; it has strong connection ability, a general computer can connect 127 peripherals, and you can connect more on your computer through the hub USB1.0, using unshielded twisted pair, the transmission speed can reach 1.5Mbps, if shielded twisted pair is used, it can reach 12Mbps, and the transmission speed of USB2.0 can reach 480Mbps; the standard is unified, the introduction of the usb standard It reduces the current PC requirements for all standard interfaces. Our daily mouse, keyboard, and printer can be marked with usb to connect to the system, thereby reducing the need for PC slots; the connection cable is light and the power supply is small. usb adopts 4-core cable, two for signal connection, two for power supply and grounding, which can provide 5V DC current to peripherals; strong vitality, open industry standard without patent copyright
You can learn more about the details of the above bus standards on the Internet
-
bus control