KEYBOARD AND DISPLAY INTERFACE - 8279

AIM:

            To write a program to study 8279 Keyboard and display controller and also initialize 8279 for rolling message in the display.

 APPARATUS REQUIRED:

            1. 8085 – Microprocessor kit        

            2. 8279 – Keyboard and display controller board

            3. Flat ribbon cable

ALGORITHM:

DISPLAY THE ROLLING MESSAGE:

1. Start the program

            2. Set mode and clear display is given to initialize the 8279

            3. The data to be displayed is moved to a register

            4. Initialize the counter value

            5. Increment the address, which is to be displayed and display the next value

            6. Decrement the counter value

            7. Delay the sequence of data that are displayed for a lively display

1.      End of the program

DESCRIPTION:    

            In the 8279 Keyboard and display interfacing we have to initialize it through the keyboard / display mode set by which we adopt the mode by which we are going to operate the clear display is executed to clear all the rows of the display RAM the data which is to be displayed is fetched and then thus are displayed is fetched and then thus are displayed at first digit of display a counter is initialized and its value is decremented until all the values are displayed A delay which is set such that the display it is delayed for a period such that to get a lively display the write display RAM Command word is used it set the auto increment flag.

 PROGRAM

            ROLLING DISPLAY:

                                    ORG 4100 H             CNT EQU OCZH

                                    DAT EQU OCOH     POINTER EQU 412CH

ADDRESS	OPCODES	LABELS	MNEMONICS	COMMENTS
4100	21,2C, 41	START	LXI H, POINTER	Set the point for data in array
4103	16,OF		MVI D, 0F H	Move immediate D register
4105	3E, 10		MVI A, 10H	Move 10 to A register
4107	D3, C2		OUT CNT	Set mode of display
4109	3E,CC		MVI A, OCCH	Clear display
410B	D3, C2		OUT CNT	Out the control word
410D	3E, 90		MVI A, 90H	Write display
410F	D3, C2		OUT CNT
4111	7E	LOOP	MOV A, M	Move the HL pair to accumulator
4112	D3, C0		OUT DAT	Clear loop RAM
4114	CD, 1F, 41		CALL DELAY	Call display 411f
4117	23		INX H	Increment HL pair
4118	15		DCR D	Decrement D register
4119	C2, 11,41		JNZ LOOP	Jump on zero
411C	C3, 00,41		JMP START
411F	06,A0	DELAY	MVI B, OFFH
4121	0E,FF	LOOP1	MVI C, FFH
4123	0D	LOOP2	DCR C	Decrement C register
4124	C2, 23,41		JNZ LOOP2	Jump on zero
4127	05		DCR B	Decrement B register
4128	C2, 21,41		JNZ LOOP1	Jump on zero
412B	C9		RET	Return
412C	FFFFFFFF
4130	FFFFFFFF
4134	98687CC8
4138	1C29FFFF

ROLLING DISPLAY:

                        HELP US

H – a=0, b=1, c=1, D=0, e=1,f=1, g=1      E – a=1, b=0, c=0, D=1, e=1, f=1, g=1

L – a=0, b=0, c=0, D=1, e=1, f=1, g=0     P – a=1, b=1, c=0, D=0, e=1, f=1, g=1

U – a=0, b=1, c=1, D=1, e=1, f=1, g=0     S – a =1, b=0, c=1, D=1, e=0, f=1, g=1

RESULT:

Thus the Program of Interfacing 8279 Keyboard and display is executed and verified.