Page 55 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Unit 3: Assembly Language Programming of 8085

An assembly program to multiply a number by 8 Program Notes
MVI A, 30H
RRC
RRC
RRC
OUT PORT1
HLT
An assembly program to find greatest between two numbers Program
MVI B, 30H
MVI C, 40H
MOV A, B
CMP C
JZ EQU
JC GRT
OUT PORT1
HLT
EQU: MVI A, 01H
OUT PORT1
HLT
GRT: MOV A, C
OUT PORT1
HLT

Fetching an Instruction

et us assume that we are trying the instruction at memory location 2005. That means that
Lthe program counter is now set to that value.
The following is the sequence of operations:
• The program counter places the address value on the address bus and the controller issues
an RD signal.
• The memory’s address decoder gets the value and determines which memory location is
being accessed.
• The value in the memory location is placed on the data bus.
• The value on the data bus is read into the instruction decoder inside the microprocessor.

• After decoding the instruction, the control unit issues the proper control signals to perform
the operation.

Questions:
1. Summarise the tuning signals.
2. Explain Demultiplexing AD7-AD0.

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