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Expt. No. 15

Title :- 8279 Keyboard and Display Controller.

Proble !tateent :- "rite 8#8$ %&P to initiali'e 8279 and to display ()ara(ters in ri*)t

entry ode. Pro+ide also t)e ,a(ility to display.

1 C)ara(ter in le,t entry ode.

2 ollin* display

/ 0las)in* display.

%:- Write 8086 ALP to initialize 8279 and display characters in

a) Right entry mode

) Le!t entry mode

c) Rolling display

d) "lashing display#

T)eory:-

Keyboard ode:-$

1 De(oded s(an ode::

%n decoded mode the internal decoder decodes the least signi!icant t&o its o! scan lines

internally to pro'ide !o(r possile cominations on the scan lines *L0 to *L+),

0$0$0$0

.h(s the o(tp(t o! decoded scan is acti'e lo .hese !o(r acti'e lo& o(tp(t lines can e also

(sed to inter!ace !o(r digit se'en segment displays$ 8 / matri1 eyoard eliminating the

e1ternal decoder#

2 En(oded s(an ode.:

%n encoded mode$ the scan co(nter pro'ides the inary co(nt !rom 0000 to on the !o(r

scan lines *L0 to *L+) &ith acti'e high o(tp(ts# .his inary co(nt m(st e e1ternally

decoded to pro'ide 6 scan lines#

3isplay can (se all 6 lines to inter!ace 6 digit se'en segment display$ (t ey oard can

(se only eight scan lines o(t o! 6 scan lines#

Display odes:-

1 i*)t Entry:-

%n the right entry mode$ 8279 displays characters !rom right to le!t in m(ltiple1ed display

lie calc(lator# .he !irst entry displayed is on the right most display# .he ne1t entry is also

displayed on rightmost display a!ter the display is shi!ted le!t y one character#

2 &e,t Entry:-

%n le!t entry mode$ 8279 displays characters !rom le!t to right in m(ltiple1ed display lie a

type&riter# %n this$ each display position is directly corresponds to a yte or nile in the

display RA4# Address 0 in the RA4 is le!tmost displayed character and address 5 is

rightmost displayed character#

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Deterination o, (odes !tored at 2###:

a

f g B

e C

d . dp

.he 7 segment displays (sed are common cathode type# *o to glo& the segment$ send logic to thesegment#

.he code can e !o(nd as,

Di*it to be

DisplayedD7 D$ D5 D3 D/ D2 D1 D#

4ex (ode

&ED se*ent d ( b a , * E dp

0 0 0 6

0 0 0

0 0 0 0 0 6

0 0 7

!E&ECTN %DDE!!E! 0 8279 %E:

% CNT& "D E6!TE : /14

D%T% PT : /#4

Di,,erent (oand ords o, 8279 sed in t)e pro*ra are:1 Key board Display ode set (oand ;###

.his command is (sed to program operating modes o! eyoard and display# .he Least

*igni!icant + its decides the eyoard mode and ne1t 2 its decides the display mode

D7 D$ D5 D3 D/ D2 D1 D#

# # # D D K K K

K K K Key board odes

0 0 0 ncoded scan eyoard 2 ey loc o(t

0 0 3ecoded scan eyoard 2 ey loc o(t0 0 ncoded scan eyoard ey roll o'er

0 3ecoded scan eyoard ey roll o'er

0 0 ncoded scan sensor matri1

0 3ecoded scan sensor matri1

0 *troe inp(t encoded display scan

*troe inp(t 3ecoded display scan

D D Display odes

0 0 8:8 it character display le!t entry

0 6:8 it character display le!t entry

0 8:8 it character display right entry 6:8 it character display right entry

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2 "rite Display % (oand ord;1##

.o &rite data into display RA4 it is necessary to set 8279 in &rite display RA4 mode

D7 D$ D5 D3 D/ D2 D1 D#

1 # # % % % % %

% T: 1: Enables %to in(reent ode

#: Disable %to in(reent ode%%%%: !pe(i,ies t)e address o, 1$ byte display %

/ Clear Coand ;11#

%t is (sed to clear all the ro&s o! display RA4 &ith a select tale laning code$ to clear the

stat(s o! "%"; RA4 and to reset interr(pt o(tp(t line#

D7 D$ D5 D3 D/ D2 D1 D#

1 1 # CD2 CD1 CD# C0 C%

CD1 CD# lan

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Pro*ra,

&abel Pro*ra Coent

4;? L$ 0 *et co(nter !or !o(r ytes

4;? AL$ 0 ontrol Word initialization

;@. +$AL

4;? /$ 2000 *et a memory pointer

4;? AL$ 90 %nitialization o! &rite display RA4 commend &ord;@. +$AL

@P, 4;? AL$ B/C Det !irst data

;@. +0$ AL ;(t data to data port

ALL +000 all delay

% / %ncrement memory pointer

3 L 3ecrement co(nter

EF @P

%. +

Delay otine: Entered at /###

&abel Pro*ra Coent

4;? 3/$ """"= Load a 3elay co(nter

@P, 3 / 3ecrement and chec &hether it is zero

EF @P

R.

Conne(tion:-

Note: a

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;@. +$AL



ALL +000 all delay



EF @P

%. +


&abel Pro*ra Coent

4;? =$ 02=

@P2, 4;? 3/$ """"= Load a 3elay co(nter

@P, 3 /

3 =

EF @P

EF @P2R.

Conne(tion:-

1 Conne(t D@N% KD!P to D@N%8$

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EF @P

ALL +000

4;? AL$ ontrol &ord !or laning display

;@. +$AL

ALL +000

E4P @P


&abel Pro*ra Coent


@P, 3 / 3ecrement to chec &hether it is zero

EF @P

R.

Conne(tion:-

1 Conne(t D@N% KD!P to D@N%8$

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E4P @P


&abel Pro*ra Coent


@P, 3 / 3ecrement to chec &hether it is zero

EF @PR.

EF @P2

R.

Data entry: eBired 4ex Codes at 2###4 to 2##/4 and ,ro 2##34 to 2##04 store

##4

Code C)ara(ters to display

6 d

>6 n

7 a

Conne(tion:-

Note: a

15 expt_8279

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