- Memory interfacing in microprocessor systems involves two main types of memory: read-only memory (ROM) and random access memory (RAM). - Memory is made up of semiconductor devices with each bit stored in a memory cell consisting of transistors. The capacity of a memory chip depends on the number of address pins determining the number of memory locations and data pins determining the number of bits stored per location. - The two major types of memory are RAM, which can be read from and written to, and ROM, which can only be read from. Common ROM types include PROM, EPROM, and EEPROM, while common RAM types are SRAM and DRAM.

1. Microprocessor & its Applications
Module 4
Memory & I/O Interfacing
Dr. Girisha G S
Dept. of CSE
SoE, DSU, Bengaluru 1

2. Memory Interfacing in 8086
- Every microprocessor-based system has a memory system
- Almost all systems contain two main types of memory:
- read-only memory (ROM) and
- random access memory (RAM) or read/write memory.
MEMORY DEVICES
- Memory is simply a device that can used to store information
- Semi conductor memories are extensively used
- Each bit of binary data is stored in a tiny circuit called a memory cell consisting of one
to several transistors.
Memory capacity
The number of bits that a semiconductor memory chip can store is called a chip capacity

3. Memory Organization
- Each memory chip contains 2N locations, where N is the no of address pins on the chip
- Each location contains M bits, where M is the no of data pins on the chip
- The entire chip will contain 2N × M bits
E.g For 4K × 4 , 212= 4096 memory locations, each location holds 4 its
So, N=12 , M=4
Two major types
– RAM (Random-access memory): Read + Write
– ROM (Read-only memory): perform only read operation
Types of ROM
- PROM
- EPROM
- EEPROM
Types of RAM
- SRAM
- DRAM

4. Memory Pin Connections
• Address Connections: select a memory location
where N is the total number of address pins
- The number of address pins is related to the
number of memory locations
Example: The 2K memory
o It has 11 address lines.
o The labels are (A0 - A10).
o If the start address is 10000H
so the end address is:
10000H + ((2*1024)10 = 800H)=107FFH

5. • Data Connections: input/output bidirectional connections
• Selection Connections : selects or enables memory devices
- The number of data pins is related to the size
of the memory location
- They are used to enter the data for storage or
extract the data for reading.
Example: An 8-bit wide (byte-wide) memory device has
8 data pins labelled D0 through D7
- Memory devices are defined by memory locations
times bit per location.
Examples: 1K × 8, 16K ×1, 64K × 4.
• Control connections:
- All memory devices have some form of control input or inputs.
- For ROMs, an Output Enable (𝑂𝐸) or Gate (𝐺 ) is present.
- For RAMs, a read-write(R/𝑊 ) or write enable(𝑊𝐸) and read enable(𝑂𝐸) are present.

6. Memory Address Decoding