Results (
Thai) 1:
[Copy]Copied!
Because of this sharing, the bus protocol (set of usage rules) is very important.Figure 4.2 shows a typical bus consisting of data lines, address lines, controllines, and power lines. Often the lines of a bus dedicated to moving data arecalled the data bus. These data lines contain the actual information that must bemoved from one location to another. Control lines indicate which device has permissionto use the bus and for what purpose (reading or writing from memory orfrom an I/O device, for example). Control lines also transfer acknowledgmentsfor bus requests, interrupts, and clock synchronization signals. Address lines indicatethe location (in memory, for example) that the data should be either readfrom or written to. The power lines provide the electrical power necessary. Typicalbus transactions include sending an address (for a read or write), transferringdata from memory to a register (a memory read), and transferring data to thememory from a register (a memory write). In addition, buses are used for I/Oreads and writes from peripheral devices. Each type of transfer occurs within abus cycle, the time between two ticks of the bus clock.Due to the different types of information buses transport and the variousdevices that use the buses, buses themselves have been divided into differenttypes. Processor-memory buses are short, high-speed buses that are closelymatched to the memory system on the machine to maximize the bandwidth(transfer of data) and are usually very design specific. I/O buses are typicallylonger than processor-memory buses and allow for many types of devices withvarying bandwidths. These buses are compatible with many different architectures.A backplane bus (Figure 4.3) is actually built into the chassis of themachine and connects the processor, the I/O devices, and the memory (so alldevices share one bus). Many computers have a hierarchy of buses, so it is notuncommon to have two buses (for example a processor-memory bus and an I/Obus) or more in the same system. High-performance systems often use all threetypes of buses.
Being translated, please wait..
