5.3 Microprocessors III: 8085 Application Examples · 2013. 11. 6. · 8085 Application Examples In the previous sequence, 8085 architecture and instructions set were presented In

5.3 Microprocessors III:

8085 Application Examples

Dr. Tarek A. TutunjiMechatronics Engineering Department

Philadelphia University

8085 Application Examples

In the previous sequence, 8085 architecture and instructions set were presented

In this presentation, we will use the 8085 for simple systems which will involve Switches, LED’s, and DC Motor

In each example, a schematic block diagram will be drawn and the assembly code will be provided

Example 1: LEDs

Example: Use the 8085 to turn on LEDs. The 8085 should be connected to eight LEDs at address 01H and the program should turn on LEDs 5,6, and 7

Solution: The 8-bit data lines are connected to the LEDs through an output latch addressed at 01H.

8085

+5V

Decoder

Latch ...

.

.

.

.

.

.

.

.

.

Address LinesA0 A7

Data LinesD0 D7

Control LinesIO/M, WR

D0

D1

D7

LED1

LED2

LED8

Enable

.

.

.

Clock

Example 1: LEDs

Data Bus: D7 D6 D5 D4 D3 D2 D1 D0LEDs: 8 7 6 5 4 3 2 1

Off On On On Off Off Off OffBits sent 0 1 1 1 0 0 0 0

Assembly Code

Mnemonic Machine Code

1000 MVI A,70H 3E % Accumulator A = 70H = 0111 00001001 701002 OUT 01H D3 % Send value in A to port 011003 011004 HLT

Example 2:

Switches & 7-segment DisplayExample: Design system using 8085 interfaced with 2

switches (address F0) and 7-segment display (address F6).

+5V

8085

+5V

Decoder

Latch ...

.

.

.

.

.

.

Address LinesA0 A7

Data LinesD0 D7

Control LinesIO/M, WR, RD

D0

D1

D7

A

B

DP

Enable

.

.

.

Clock

TriStateBuffer

Enable

D0

D1

+5VSW1

SW2

Example 2:

7-segment DisplayWrite an assembly code that continuously displays ‘0’

If switch 1 is closed, program should display ‘1’ and stop

If switch 2 is closed, program should display ‘2’ and stop

DP G F E D C B A

D7 D6 D5 D4 D3 D2 D1 D0

0 0 1 1 1 1 1 1 3F display ‘0’

0 0 0 0 0 1 1 0 06 display ‘1’

0 1 0 1 1 0 1 1 5B display ‘2’

Example 2. Assembly CodeLoop MVI A,3F % Accumulator A = 3F, to display ‘0’

OUT F6 % send result to display address F6IN F0 % Read switches at address F0ANI 01 % Mask with bit 0 first switchSUI 01 % Sub from 1 (i.e. check if closed)JZ xx % If result = 0 go to address xxIN F0 % Read switches at address F0ANI 02 % Mask with bit 1 second switchSUI 02 % Sub from 2 (i.e. check if closed)JZ yy % If result = 0 go to address yyJMP Loop % Jump back to Loop

xx MVI A, 06 % Accumulator A = 06, to display ‘1’OUT F6 % send result to display addressHLT % stop

yy MVI A, 5B % Accumulator A = 5B, to display ‘2’OUT F6HLT % stop

Example 3: DC Motor

Example: Design a mechatronics system that uses the 8085 and Pulse Width Modulation (PWM) to turn a DC Motor at a speed of 60 RPM. Use the following specifications:• Connect the motor with latch at address 88• Microprocessor clock is 4 MHz• Motor maximum speed is 300 RPM

8085

+5V

Decoder

Latch

Address LinesA0 A7

Data Lines, D0

Control LinesIO/M, WR

Enable

Clock

M

+Vcc

Example 3: PWM

Pulse Width Modulation (PWM) is a common method to control the speed of a DC motor

A power transistor (Q) working as a switch is connected to the motor• If Q is always ON Motor will turn at maximum speed

(assuming no load)

• If Q is sometimes ON Motor will turn at %timeON x max speed (i.e. speed = duty cycle x max speed)

In our example, 60 RPM/300 RPM = 0.2 write program to get duty cycle of 20%

Example 3. Assembly Code

Loop MVI A,00 % Bit0 off Q off

OUT 88 % motor address ‘88’MVI C,FF % C = (FF) H

Back1 DCR C % Decrement C by 1JNZ Back1 %Delay for time Q offMVI A,01 % Bit0 ON Q on

OUT 88MVI C, Count % C = (Count) H

Back2 DCR C % Decrement C by 1JNZ Back2 % Delay for time Q onJMP Loop

Time delay calculationsTime delay when Q off, (1/4 MHz) x (14 cycles) x 255 = 892.5 ms Total Time (on + off), T = 892.5/0.8 = 1115.6 msTime delay when Q on, 0.2(1115.6 ms)= (1/4 MHz) x (14 cycles) x N

N =64 Count = (40)H

Summary

Three applications for 8085 were presented

• LED

• Switches and 7-segment display

• DC Motor

For each exam, the block diagram and assembly code were provided