Digital Clock 8255 Interface

INTRODUCTION.

A clock is an instrument that is used to indicate and keep time. There are two categories of clock depending on how they display time, analog clock and digital clock. A digital clock can be designed using microprocessor. Microprocessor has a lot of application such as, it can be used in industries for temperature control, stepper motor control and also can be used to control traffic light. All of this applications required to be during a specific time of the day, for example switching ON and OFF the traffic lights at a specific time during a day or to keep track of the workers by punching entry time and exit time for each worker. All this application requires digital clock which is able to display the time in terms of hours, minutes and seconds. A digital clock can be displayed on the LCD screen. LCD screen is the type of the screen which is used for digital clock display and many portable computer devices. The figure below shows LCD screen.

Figure 1: LCD screen

In order for microprocessor to communicate with the real word an 8255 programmable peripheral interface is used. An 8255 is a general purpose Programmable Peripheral Interface (PPI) provided on the board of MP85 to enable the user to interface any real world application to the microprocessor. It has three 8-bit parallel ports that can be configured individually as input or as output depending on the requirement. The chip has been used in I/O mapped mode and has an address of (A0-A7).

This report explain about the experiment conducted in the lab to design a program which is used by a microprocessor 8085 to display hours, minutes and seconds on the LCD screen.

OBJECTIVES OF THE EXPERIMENT.

• To develop a program for digital clock.

• To interface microprocessor and LCD screen using 8255 programmable peripheral IC

FLOW CHART.

Figure 2: Flow chart

PROGRAM.

Table 1 - main program

ADDRESS OPCODE LABEL MNEMONICS COMMENT

8000 31, 00, 8A LXI Load content of 8A00 to SP

8003 06, 00 L3 MVI move immediately 00 to B

8005 0E, 00 MVI move immediately 00 to C

8007 26, 00 MVI move immediately 00 to H

8009 CD, 00, 87 CALL Call INI

800C 3E,