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Microprocessor
Dr. Rabie A. RamadanAl-Azhar University
Lecture 5
Interfacing Memory
An address should be placed on the
address lines.
The low-order address lines are
decoded by the internal decoder of the
memory chip, and the addressed
register is identified.
The high-order address should be
decoded to generate a Chip Select
signal, and the memory chip is
selected by asserting the Chip Select
low.
2
CS
Interfacing Memory
To read from the addressed register, the
should be asserted low to enable the output
buffer, and then the data byte from the
register will be placed on the I/O lines.
To write into the addressed register, the
should be asserted low to enable the input
buffer, and then data bits from the data
lines are stored into the register.
3
RD
WR
How does the Z80 Read from or
Write into Memory?
4
Basic Concepts in Memory
Interfacing
Interface Function:
• Be able to select the chip
• Identify the register
• Enable the appropriate buffer.
5
Read from the Memory
6
Write into memory register
7
Address Decoding
3 input lines A0-A2 (Memory Select Buffer (MSB))
A3 – A7 are control lines since the address starts at F0H to F7H
3 lines enable only one o/p line
8 memory chips can be controlled
8
A7 A6 A5 A4 A3 A2 A1 A0
1 1 1 1 0 1 1 1= F7H
Example 1: Interfacing the 2764
EPROM
Used in industry to develop
microprocessor-based products.
8k (8192 8) memory chip with
8 data lines
Housed in a 28-pin package.
9
Chip Configuration
10
What is the Memory Addresses Range?
11
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
0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1
0000H 1FFFH
Interfacing CMOS 6116 Static R/W
Memory
This is a 2k static memory chip
organized as 2048 8 format.
It has 11 address lines (A10-A0),
8 data lines
3 control signals:
12
Chip Configuration
13
Memory Interface
What is the addresses range? Assume A12 and A11 are do not care .
14
A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
1 0 0 X X 0 0 0 0 0 0 0 0 0 0 0
1 0 0 X X 1 1 1 1 1 1 1 1 1 1 1
8000 87FF -- Address ranges may differ due to the do not care at A12 and A11