memory organi.pptx

MEMORY MPMC

1. Memory Organization of 8085 Microprocessor

2. Memory Organization of 8085 A microprocessor system requires both RAM (Random Access memory) and EPROM (Erasable Programmable Read Only Memory ). Hence the memory space has to be divided between RAM and EPROM. (Erasable-Programmable Read Only Memory ). The 8085 microprocessor has 64 K bytes of addressable memory space and allocating this address space for RAM and EPROM depends on the applications. Some system may require large memory space. But some system requires less memory space and in this case the full memory space will not be utilized .

3. Memory Organization of 8085 Then the unused memory address can be used for addressing I/O devices such I/O devices are called memory mapped I/O devices. In EPROM is used as a program memory and RAM is used as a data memory when EPROM and RAM are used, the total 64 Kbytes address space is shared by them. For an example the address map of a 64 Kbytes memory space which can be used by the microprocessor as shown in figure.3.1 The entire 64 K bytes of address space is divided into four subsets.

4. Memory Organization of 8085 The first subset of 8 Kbytes of addresses are assigned to the EPROM i.e., address range from 0000H to IFFFH. The next 48 Kbytes of addresses assigned to RAM i.e., address range from 2000H to DFFFH. The next highest 2 Kbytes to input/output devices i.e., address range from E000H to E7FFH and the remaining 6K bytes are un used i.e., the address range from E800H to FFFH. The separate decoding circuit decides the address map of the entire address space.

5. Memory Organization of 8085

6. MEMORY MAPPING A memory map is a pictorial representation of memory devices are located in the entire range of address.   The number of address lines of the microprocessor unit determines its memory capacity. The 8085 Microprocessor unit has 16 address lines and it capable of indentifying 2^16 = 64 k bytes (65, 536) memory registers.   The entire memory address can range from 0000 to FFFF in Hex. Memory address provide the locations of various devices in the system. The 8085 microprocessor can access 64 Kbytes memory but it is not necessary to use full 64 Kbytes address space, so the total memory size depends upon the various applications.

7. A typical memory map is shown in figure.3.2

8. I/O MAPPING (INPUT/OUTPUT MAPPING) I/O Mapping is defined as the assignment of addresses to various I/O devices in a memory chip. The microprocessor unit can identify and communicate with the I/O devices by using two methods. 1. Memory Mapped I/O 2. I/O Mapped I/O

9. 1. Memory Mapped I/O In memory mapped I/O, the Input / Output devices are indentified with a 16 bit addresses. In 8085 microprocessor the 64 Kbyte memory map is shared between memory and I/O devices. The address assigned for l/o device can not be used for memory register. The memory related Instructions (such as STA, LDA, MOV R,M, MOV M,R) are used to data transfer between microprocessor and I/O devices. A 64 Kbyte address space memory mapped I/O is shown in figure.3.3

10. Memory Mapped I/O

11. Memory Mapped I/O

12. In the above figure 3.4, there are four address spaces in the 64 k byte of memory mapped I/O. The Lowest 8 k byte address are allotted to the EPROM. The next highest 48 k byte addresses are allotted to the RAM. The next highest 2 k byte addresses are allotted to I/O port and remaining 6 k byte addresses are unused.

13. Advantages of Memory Mapped I/O 1. It provides more input and output ports. 2. High Speed. 3. Powerful instructions are used to access I/O device. 4. No special instructions are needed. Disadvantages of Memory Mapped I/O 1. Length of program is increased 2. Increased interface hardware 3. Limited number of I/O ports connected 4. Less memory requirement

14. 2. I/O Mapped I/O In I/O mapped I/O, the devices have separate addresses. The microprocessor unit uses 8-address lines to identify the microprocessor. The microprocessor can identify 256 input devices and 256 output devices (2 8 = 256) The input and output devices are differented by the control signals I/O Road (IOR) and I/O write (IOW). In this method, I/O addresses range from 00H to FFH. A 64 k byte address space for I/O mapped I/O is shown in figure.3.5

15. I/O Mapped I/O

16. I/O Mapped I/O

17. I/O Mapped I/O The 8085 microprocessor has two instructions. (IN & OUT) It can be used for data transfer between I/o device and the processor. When IN instruction is used to data transfer from the accumulator to an output device.

18. Advantages of I/O mapped I/O 1. Simple program. 2. Memory address is not affected by I/O. 3. More space for memory. Disadvantages of I/O mapped 1/0 1. It is less powerful less flexible than Memory mapped I/O 2. Two additional control lines are needed for issuing IOR and IOW signals.