8051 microcontrollers

Example 8.2 Assume the following values for the system of Figure 8.14: Length of the virtual address field =32 bits Length of the segment number field = 12 bits Length of the page number field = 8 bits Length of the displacement field = 12 bits Now, determine the value of the physical address using the following information: Value of the virtual address field=000FA0BA 16 Contents of the segment table address (000) 16 = OFF 16 Contents of the page table address (IF9 16 ) = AC 16 Solution From the given virtual address, the segment table address is 00016 (three high-order hexadecimal digits of the virtual address). It is given that the contents of this segment-able address is OFF 16• Therefore, by adding the page number p (fourth and fifth hexadecimal digits of the virtual address) with OFF 16,the base address of the page table can be determined as: 0FF 16 + FA 16 = 1F9 16 Since the ...

8.1.3 Virtual Memory and Memory Management concepts Due to the massive amount of information that must be saved in most systems, the mass storage device is often a disk. If each access is to a disk (even a hard disk), then system throughput will be reduced to unacceptable levels. An obvious solution is to use a large and fast locally accessed semiconductor memory. Unfortunately the storage cost per bit for this solution is very high. A combination of both off-board disk (secondary memory) and on-board semiconductor main memory must be designed into a system. This requires a mechanism to manage the two-way flow of infonnation between the primary (semiconductor) and secondary (disk) media. This mechanism must be able to transfer blocks of data efficiently, keep track of block usage, and replace them in a nonarbitrary way. The main memory system must, therefore, be able to dynamically allocate memory space. An operating system must have resource protection from corruption or abu...

8.1 Memory Organization 8.1.1 Introduction A memory unit is an integral part of any microcomputer system, and its primary purpose is to hold instructions and data. The major design goal of a memory unit is to allow it to operate at a speed close to that of the processor. However, the cost of a memory unit is so prohibitive that it is practically not feasible to design a large memory unit with one technology that guarantees a high speed. Therefore, in order to seek a trade-off between the cost and operating speed, a memory system is usually designed with different technologies such as solid state, magnetic, and optical. In a broad sense, a microcomputer memory system can be divided into three groups: Processor memory Primary or main memory Secondary memory Processor memory refers to a set of microprocessor registers. These registers are used to hold temporary results when a computation is in progress. Also, there is no speed disparity betw...