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Detailed Review of the 8085 Instruction Set

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8085 Instruction Set

The 8085 instructions can be classified as follows:

Data transfer operations

Arithmetic operations (ADD, SUB, INR, DCR)

Logic operations

Branching operations (JMP, CALL, RET)

• Between registers• Between memory location and a register• Direct write to a register / memory• Between I/O device and accumulator

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8085 Instruction Types

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8085 Instruction Types

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8085 Instruction Types

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Simple Data Transfer Operations

Examples:

MOV B,A 47 From ACC to REG MOV C,D 4A Between two REGs MVI D,47 16 Direct-write into REG D

47

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Simple Data Transfer Operations

Example:

OUT 05 D305

Contents of ACC sent to output port number 05.

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Simple Memory Access Operations

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Simple Memory Access Operations

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Arithmetic Operations

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Arithmetic Operations

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Arithmetic Operations

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Arithmetic Operations

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Overview of Logic Operations

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Logic Operations

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Logic Operations

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Logic Operations

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Branching Operations

Note: This is an unconditional jump operation. It will always force the program counter to a fixed memory address continuous loop !

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Branching Operations

Conditional jump operations are very useful for decision making during the execution of the program.

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Example

Write a 8085 machine code program:

Read two different memory locations

Add the contents

Send the result to output port 02 (display) if there is no overflow

Display “FF” if there is an overflow

Stop

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Example

2000 LDA 2050 3A2001 502002 202003 MOV B,A 472004 LDA 2051 3A2005 512006 202007 ADD B 802008 JNC 2013 D22009 132010 202011 MVI A,FF 3E2012 FF2013 STA 2053 322014 532015 HLT 20

Load contents of memory location 2050 into accumulator

Load contents of memory location 2051 into accumulator

Save the first number in B

Add accumulator with B

Jump to 2013 if no carry !

Direct write FF into accumulator

Store accumulator contents at 2053

Stop

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8255Features:• 3 8-bit IO ports PA, PB, PC • PA can be set for Modes 0, 1, 2. PB for 0,1 and

PC for mode 0 and for BSR. • PC has 2 4-bit parts: PC upper (PCU) and PC

lower (PCL), each can be set independently for 1 or O. Each PC bit can be set/reset individually in BSR mode.

• PA and PCU are Group A (GA) and PB and PCL are Group B (GB)

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Pin configuration

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A1 A0 Select

0 0 PA

0 1 PB

1 0 PC

1 1 Control reg.

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