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8255 Programmable Peripheral Interface
Block Diagram
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8255 Programmable Peripheral Interface
Modes of 8255
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8255 Programmable Peripheral Interface
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Control Word
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8255 Programmable Peripheral Interface
Bit definitions of the 8255 control register
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8253 Programmable Interval imer!Co"nter #PI$
Block Diagram
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8253 Programmable Interval imer!Co"nter #PI$
Control Word
CONTROL BYTE D7 - D0
D7 D6 D5 D4 D3 D2 D1 D0
SC1 SC0 RL1 RL0 M2 M1 M0 BCP
D7SC1
D6SC0
Counter Select
0 0 counter 0
0 1 counter 1
1 0 counter 2
D5RL1
D4RL0
R / L Definition
0 0 Counter v!ue "# !tc$e%& T$"# 'en#
t$t t$e #e!ecte% counter $# "t#content# trn#(erre% "nto
te')orr*
!tc$+ ,$"c$ cn t$en e re% * t$e CP.&
0 1 Re% / !o% !e#t-#"n"("cnt *te on!*&
1 0 Re% / !o% 'o#t-#"n"("cnt *te on!*&
1 1 Re% / !o% !e#t-#"n"("cnt *te ("r#t+
t$en 'o#t-#"n"("cnt *te&
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1 1 "!!e! v!ue
825% &'I()*+,- +.'C/*0'0&+ ,+.'C/*0'0&+ *)C)I()*
*,'+MI)* #&+,*$
D3
M2D2M1
D1M0
Mode value
0 0 0 'o%e 0 "nterru)t on ter'"n! count
0 0 1 'o%e 1 )ror''!e one-#$ot
1 0 'o%e 2 rte enertor
1 1 'o%e 3 #ure ,ve enertor
1 0 0 'o%e 4 #o(t,re tr"ere% #troe
1 0 1 'o%e 5 $r%,re tr"ere% #troe
D0 counts down in
0 "nr*
1 BCD
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Block Diagram
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825% &'I()*+,- +.'C/*0'0&+ ,+.'C/*0'0&+ *)C)I()*
*,'+MI)* #&+,*$
Bit config"ration of Mode Instr"ction #,s1nchrono"s$
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825% &'I()*+,- +.'C/*0'0&+ ,+.'C/*0'0&+ *)C)I()*
*,'+MI)* #&+,*$
Bit config"ration of Mode Instr"ction #+1nchrono"s$
825% &'I()*+,- +.'C/*0'0&+ ,+.'C/*0'0&+ *)C)I()*
*,'+MI)* #&+,*$
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Bit config"ration of Command
825% &'I()*+,- +.'C/*0'0&+ ,+.'C/*0'0&+ *)C)I()*
*,'+MI)* #&+,*$
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Bit config"ration of +tat"s Word
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825 Programmable Interr"pt Controller
Block Diagram
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ICW1 (Initialisation Command Word One)
A0
0
D7 D6 D5 D4 D3 D2 D1 D0
A7 A6 A5 1 LTIM ADI SNGL IC4
D0: IC4: 0=no ICW4, 1=ICW4 required
D1: SNGL: 1=Sin!e "IC, 0=C#$%#ded "IC
D2: ADI: Addre$$ in&er'#!( )$ed on!* in +0+5, no& +0+6(
1=IS-$ #re 4 .*&e$ #/#r& 0200,
0204, e&% 0=IS-$ #re + .*&e #/#r& 0200, 020+,
e&%
D3: LTIM: !e'e! &riered in&erru/& ode: 1=A!! I !ine$
!e'e! &riered( 0=ede &riered
D4D7: A5A7: +0+5 on!*( IS #ddre$$ !oer .*&e $een&( Te
!oer .*&e i$
A7 A6 A5 A4 A3 A2 A1 A0
o i% A7, A6, A5 #re /ro'ided .* D7D5 o ICW1 i ADI=1, or A7, A6
#re /ro'ided iADI=0( A4A0 or A5A0 #re $e& .* +25 i&$e!:
ADI=1 $/#%in 4 .*&e$
I8 A7 A6 A5 A4 A3 A2 A1 A0
I0 A7 A6 A5 0 0 0 0 0
I1 A7 A6 A5 0 0 1 0 0
I2 A7 A6 A5 0 1 0 0 0
I3 A7 A6 A5 0 1 1 0 0
I4 A7 A6 A5 1 0 0 0 0
I5 A7 A6 A5 1 0 1 0 0
I6 A7 A6 A5 1 1 1 0 0
I7 A7 A6 A5 1 1 1 0 0
ADI=0 $/#%in + .*&e$
I8 A7 A6 A5 A4 A3 A2 A1 A0
I0 A7 A6 0 0 0 0 0 0
I1 A7 A6 0 0 1 0 0 0
I2 A7 A6 0 1 0 0 0 0
I3 A7 A6 0 1 1 0 0 0
I4 A7 A6 1 0 0 0 0 0
I5 A7 A6 1 0 1 0 0 0
I6 A7 A6 1 1 0 0 0 0
I7 A7 A6 1 1 1 0 0 0
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ICW2 (Initialisation Command Word Two)
9ier .*&e o IS #ddre$$ +0+5, or + .i& 'e%&or #ddre$$
+0+6(
A0
1
D7 D6 D5 D4 D3 D2 D1 D0
A15 A14 A13 A12 A11 A10 A A+
ICW3 (Initialisation Command Word Three)
A0
1
D7 D6 D5 D4 D3 D2 D1 D0
M#$&er S7 S6 S5 S4 S3 S2 S1 S0
S!#'e 0 0 0 0 0 ID3 ID2 ID1
M#$&er ode: 1 indi%#&e$ $!#'e i$ /re$en& on &
in&erru/&, 0 indi%#&e$ dire%&
in&erru/&
S!#'e ode: ID3ID2ID1 i$ &e $!#'e ID nu.er( S!#'e 4 on I4 #$
ICW3=04
0000 0100
ICW4 (Initialisation Command Word Four)
A0
1
D7 D6 D5 D4 D3 D2 D1 D0
0 0 0 SNM ;) MI Mode
SNM: 1=S/e%i#! u!!* Ne$&ed Mode, 0=NM
M
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OCW2 (Operational Command Word Two)
A0
1
D7 D6 D5 D4 D3 D2 D1 D0
SL >I 0 0 L3 L2 L1
SL >I A%&ion
>I
0 0 1 Non $/e%ii% >I L3L2L1=000
0 1 1S/e%ii% >I %o#nd In&erru/& &o %!e#r
i'en .* L3L2L1
Au&o ro&ion o /riori&ie$L3L2L1=000
1 0 1 o&e /riori&ie$ on non$/e%ii% >I
1 0 0 o&e /riori&ie$ in #u&o >I ode $e&
0 0 0 o&e /riori&ie$ in #u&o >I ode %!e#r
S/e%ii% ro&ion o /riori&ie$ Loe$&
/riori&* IS=L3L2L1
1 1 1o&e /riori&* on $/e%ii% >I %o#nd
re$e&$ %urren& IS .i&
1 1 0 Se& /riori&* doe$ no& re$e& %urren& IS
.i&
0 1 0 No o/er#&ion
OCW3 (Operational Command Word Three)
A0
1
D7 D6 D5 D4 D3 D2 D1 D0
D7 SMM SMM 0 1 M>D I IS
SMM SMM e%&
0 No ee%&
1 0 e$e& $/e%i#! #$?
1 1 Se& $/e%i#! #$?
824 e1 board displa1 controller
Block Diagrams
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