17. memory interfacing iii
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The document discusses memory interfacing and memory mapping in microprocessors. It explains that the 8085 microprocessor can access 64KB of memory using its 16 address lines. This memory space can be divided into multiple memory chips, with the address lines used to select a specific chip using chip select lines, as well as the address within that chip. Examples are given of mapping 256-byte and 1KB memory chips into the microprocessor's address space using different combinations of address lines for chip selection and internal addressing.
17. memory interfacing iii
- 1. MICROPROCESSOR 8085 LECTURE 20 MEMORY INTERFACING-IV PROF. SANDIP DAS
- 2. MEMORY MAP • Number of Address lines in 8085= 16 • Hence, can identify 216=65,536 memory registers, each with a 16 bit address. • Thus, we can say 8085 can identify 64KB of memory, which can range from 0000-FFFF addresses. • These 64K addresses are assigned to memories and I/O devices. • A memory map is a pictorial representation in which memory devices are located in the entire range of addresses. • Memory addresses provide the locations of various memory devices in the system. • Interfacing logic defines the range of memory addresses for each memory device. Register 65536 Register 3 Register 2 Register 1 FFFF 0001 0000 0002
- 3. IF WE HAVE MEMORY CHIPS OF 256 REGISTERS THEN WE NEED 256 CHIPS TO MAKE 65,536 REGISTERS 256 registers 0r 256x8 256 registers 0r 256x8 256 registers 0r 256x8 256 registers 0r 256x8 0000-00FF 0100-01FF 0200-02FF FF00-FFFF Memory chip 1 Memory chip 2 Memory chip 3 Memory chip 256
- 4. LET US ASSUME WE HAVE MEMORY CHIPS WITH 256 REGISTERS AND NEED TO ACCESS ADDRESS RANGE OF 0000-00FF • So, we need only 256 registers (out of 65,536) each of 8bit (since 8085 is 8 bit Microprocessor). • Thus, to address 256 registers we require eight lines (since, 28=256). • Remaining eight address lines are used selecting a specific chip or in other words we can say it is used as a chip select 𝐶𝑆 signal. A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 =0000 H 1 1 1 1 1 1 1 1 =00FF H Register Select Chip Select
- 5. MEMORY MAPS: 256 BYTES OF MEMORY 256 registers 0r 256x8 A7 A0 Eight I/O lines 𝑅𝐷 𝑊𝑅𝐶𝑆 Internal Decoder 𝑀𝐸𝑀𝑅𝐷 𝑀𝐸𝑀𝑊𝑅 A15 A8 Memory address of this chip ranges from 0000-00FF.
- 6. NOW SUPPOSE WE WANT TO SELECT ANOTHER ADDRESS RANGE WITHIN THE MEMORY MAP A15 A14 A13 A12 A11 A10 A9 A8 0 1 0 0 0 0 0 0 A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 =4000 H 1 1 1 1 1 1 1 1 =40FF H Register Select Chip Select =40H
- 7. MEMORY MAPS: 256 BYTES OF MEMORY 256 registers 0r 256x8 A7 A0 Eight I/O lines 𝑅𝐷 𝑊𝑅𝐶𝑆 Internal Decoder 𝑀𝐸𝑀𝑅𝐷 𝑀𝐸𝑀𝑊𝑅 A15 A8 Memory address of this chip ranges from 4000-40FF. A14
- 8. MEMORY ADDRESS RANGE OF 1KB MEMORY 1 KB= 1024x8=210x8 Thus, we see memory chip with 1KB memory consists of 1024 registers which requires 10 address lines to identify each register. A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 =0000 H 1 1 1 1 1 1 1 1 1 1 =03FF H Register Select Chip Select
- 9. MEMORY MAPS: 1KB OF MEMORY 1024 registers 0r 1024x8 A9 A0 Eight I/O lines 𝑅𝐷 𝑊𝑅𝐶𝑆 Internal Decoder 𝑀𝐸𝑀𝑅𝐷 𝑀𝐸𝑀𝑊𝑅 A15 A10 Memory address of this chip ranges from 0000-03FF. A14