Keybrd Interface Class

7/24/2019 Keybrd Interface Class

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Interfacing Keyboard with 8086

Interface a 4 * 4 keyboard with 8086 using 8255 an writean ALP for detecting a key closure and return the key codein AL !he debounce "eriod for a key is #0$s %se softwaredebouncing techni&ue '()%+,( is an a-ailable #0$sdelay routine

.olution: Port A is used as output port for selecting a row of keyswhile Port B is used as an input port for sensing aclosed key. hus the keyboard lines are selected one by

one through port A and the port B lines are polledcontinuously till a key closure is sensed. he routine

!"B#$%&" is called for key debouncing. he key

code is depending upon the selected row and a lowsensed colu'n.



Interfacing ()( Keyboard




• he higher order lines of port A and port B are left unused.he address of port A and port B will respecti*ely 8000+ and800,+ while address of &- will be 8006+. he flow chartof the co'plete progra' is as gi*en. he control word for this

proble' will be 8,+. &ode seg'ent &/ is used for storing the progra' code.

• /ey 'ebounce : -hene*er a 'echanical pushbutton is pressed or released once1 the 'echanical co'ponents of thekey do not change the position s'oothly1 rather it generates a

transient response .



ASSUME CS:CODE

CODE SEGMENT

MOVAL,82H OUT CWR,AL

MOV BL,00h ; key vale

!OR A!,A! ; "lea# all$a%&

OUT 'A,AL

Wa(): *N AL,'B

AND AL,0+

CM' AL,0+

- Wa() CALL De./"e

MOV AL,1+H

MOV BH,0 ; R/3"/)

Ne4)#/3: ROL AL,05

MOV CH,AL

OUT 'A,AL

*N AL,'B

AND AL,0+

MOV CL,0

;C/l"/)

Ne4)"/l: RCR AL,05

NC 6ey

*NC BL

DEC CL

N- Ne4)"/l

MOV AL,CH DEC BH

N- Ne4)#/3

M' Wa()

6ey: MOV AL,BL *NT 7H



De./"e 'ROC NEAR

MOV CL,0++HBa"k: NO'

DEC CL

N- Ba"k

De./"e END' CODE ENDS

Keybrd Interface Class

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