Microprocessor

Dr. Rabie A. RamadanAl-Azhar University

Lecture 4

Machine Cycles and Bus Timings

Microprocessor includes 158 different

instruction types.

• Each instruction has two parts:

• Operation code (known as opcode) and operand.

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OUT (10H), A

Opcode to

output data

Operand to specify that the

byte should be sent from the

accumulator to port 10H

Machine Cycles and Bus Timings

Assume that the instruction is stored in 2 Bytes

The Z80 has to perform three operations:

• Read Byte 1 from the first memory location

• Read Byte 2 from the next memory location

• Send Data to port 10H

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OUT (10H), A

Opcode to

output data

Operand to specify that the

byte should be sent from the

accumulator to port 10H

Machine Cycles and Bus Timings Instruction

• the time required to complete the execution of an instruction. The Z80

instruction cycle consists of one to six machine cycles or one to six

operations.

Machine Cycle

• The time required to complete one operation of accessing memory,

accessing I/O, or acknowledging an external request. This cycle may

consist of three to six T-states.

T-state

• One subdivision of operation performed in one clock period. These

subdivisions are internal states synchronized with the system clock and

each T-state is equal to one clock period.

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Opcode Fetch Machine Cycle (M1)

Address Machine Code Instruction Comment

2002 010001112 (47H) LD B, A Copy A into B

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Opcode Fetch Machine Cycle (M1)

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Opcode Fetch Machine Cycle (M1)

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The Timing of the opcode Fetch Machine

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The Timing of the

opcode Fetch Machine

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The Timing of the

opcode Fetch

Machine

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The Timing of the

opcode Fetch

Machine

Memory Read Machine Cycle

The instruction consists of two bytes;

• Opcode and Data byte.

• The Z80 must first read these bytes from memory

• Requires at least two machine cycles.

• The machine cycle is opcode fetch, and

• the second machine cycle is Memory Read

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Memory Write Cycle

This is a one-byte instruction with two machine cycles:

• Opcode Fetch and Memory Write.

• Z80 fetches the code (77H) and

• it copies the byte 9FH from the accumulator into the memory

location 2350H.

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Memory Interfacing

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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.

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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.

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RD

WR

How does the Z80 Read from or

Write into Memory?

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Basic Concepts in Memory

Interfacing

Interface Function:

• Be able to select the chip

• Identify the register

• Enable the appropriate buffer.

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Read from the Memory

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Write into memory register

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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

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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.

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Chip Configuration

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What is the Memory Addresses Range?

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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 x 8 format.

It has 11 address lines (A10-A0),

8 data lines

3 control signals:

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Chip Configuration

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Memory Interface

What is the addresses range? Assume A12 and A11 are do not care .

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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

Reading Assignment

Please Read

• Chapter 3

• Chapter 4

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