Microprocessor 8085

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