chapter 3a pic18 assemblylanguageprogrammingparta(2)

7/26/2019 Chapter 3A PIC18 AssemblyLanguageProgrammingPartA(2)

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Chapter 3

PIC18 Assembly Language

Programming

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3.1 General Assembly Language

Programming

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Outline

Machine vs. assembly language

tructure o! assembly language

"he program counter an# program

memory in PIC

ome e$ample #irectives% O&G' ()*'

(+, an# ("

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Machine an# Assembly Language

Machine Language (opcode) A se-uence o! s an# 1s that can be e$ecute#

by the processor

/ar# to un#erstan#' program' an# #ebug !or

human being

Assembly Language (Source Code)

*e!ine# by assembly instructions

Assembly programs must be translate# by anassemblerbe!ore it can be e$ecute#

re!erre# to as low-level language because the

program nee#s to 0no the #etaile#

interaction ith the CP, 4


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Machine an# Assembly Language

e.g. in PIC

Machine Co#e2Opco#e

Assembly Co#e

(34 movl $34

5(6 mov! $6' A

(*7 movl $*7

456 a##! $6' 7' A

(3 movl $3

5(5 mov! $5' A

(69 movl $69

445 a##!c $5' 7' A

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"o "ypes o! Assembly tatements

Directives 2pseudo-instruction ,se# to control the

assembler

*o not generate machineco#e

e.g.' O&G $ an# ()*

Assembly language

instructions *o generate machine co#e to

per!orm various operations

e.g.' all lines e$cept the

comments an# #irectives6


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.lst !ile

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(lements o! an Assembly Language tatement

1. Label 2Optional Must start in column 1

4. Mnemonics

Coul# either be an assembly instruction

mnemonicor an assembler directive

($amples o! Mnemonics%

false equ0: e-u is an assembler #irective loop: incf0x20, W, A: inc! is an instruction

mnemonic

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(lements o! an Assembly Language tatement

3. Operan#s 2Optional false equ 0

loop: incf 0x20, W, A

. Comment 2Optional decf 0x20, F, A ;decrement the loop

count

; the whole line is comment

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Program Memory

,se# primarily in storing assemblyinstructions' although it can be use# to

store !i$e# #ata 2loo0up table later

eparate !rom #ata memory 41;bit a##ress bus' 15;bit #ata bus

A##ress up to 441


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Program Memory

(ach PIC18 member has a 41;bit a##ress bus.

Can a##ress up to 441


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Placement o! Instructions in Program Memory

Most instructions are 4 bytes. A !einstructions are bytes.

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Program

memory

a##ress

Opco#e

Assembly

Language Co#e


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Program Counter 2PC

,se# by the CP, to point to the a##resso! the instruction being !etche#.

41;bit store# as 3 bytes PCL' PC/' PC,.

ince most instructions are 4 bytes' PC

increments by 4 in each instruction

cycle.

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7etching an# ($ecution in PIC18

"he instruction fetchstage gets the ne$tinstruction machine co#e !rom program

memory.

"he eecutionstage #oes hatever themachine co#e calls !or.

!ecution' hich involves interaction

ith the #ata memory' #oes not inter!ereith fetchinginstruction !rom the

program memory.

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PIC18 Pipelining

Instea# o! ta0ing to instruction cyclesto !irst fetchan# eecutean instruction'

both can be accomplishe# in one

instruction cycle. "his mechanism is calle#pipelining.

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7etching an# ($ecution Cycles

7etching Cycle Increment PC

7etch instruction into the instruction

register 2I& ($ecution Cycle

*eco#e instruction

&ea# operan#s !rom #ata memory Per!orm Arithmetic=Logic operation

>rite the result to the #estination.

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7etch;An#;($ecute% A Complete ?ie

17

mov! $46' >' A

4

a##l $

Decode

0x32

0x32

0x32

mov! $45' A

Decode

0x04

0x04

0x36

5

mov! $49' A

0x36

0x360x36

0x36

Decode


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ome important #irectives% (+,' ("

(+, @ associates a constant number ith ana##ress label.

e.g.' COU! equ 0x2"

##########

mo$lw COU!: >&(G < $46

(" @ i#entical to (+,' but value assigne# by ("

can be reassigne# later.

e.g.' COU! set 0x00 ###########

COU! set 0x2"

##########

mo$lw COU!: >&(G < $46 18


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>ith (+,First%e& '(U 0x0"

)ec%e& '(U 0x0*

mo$lw 0x22

mo$wf First%e&,A

mo$wf )ec%e&,A

addwf First%e&, W,A

addwf )ec%e&, W,A

(+, an# (" *irectives

>ithout (+, mo$lw 0x22

mo$wf 0x0",A

mo$wf 0x0*,A addwf 0x0", W,A

addwf 0x0*, W,A

e.g.' Move 44/ into to !ile registers itha##resses $6 an# $5' a## the contents o! all

three registers an# put the result in >&(G%

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CLOCB *irective

*e!ines a list o! name# constants. 7ormat% c+locnumD

constant labelD E%incDF

endc e.g. 1' c+loc 0x"0

test-, test2, test., test/

endc ?alues Assigne#%

test1 < $6' test4 < $61'

test3 < $64' test < $63.20


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ou shoul# be able to ...

*escribe the #i!!erence beteen machine co#e an#assembly co#e

*escribe the #i!!erence beteen #irectives an#

assembly language instructions

List the elements o! an assembly languagestatement

($plain the program memory architecture in PIC18

($amine program in the program memory in#o

o! MPLA

*escribe the role o! the program counter

*escribe the pipelining !etching an# e$ecution

mechanism in PIC18 21


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3.4 ,nsigne# an# igne#

Arithmetic' Logic Instructions

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Outline

ubtraction o! unsigne# number

igne# number arithmetic

C* a##ition

Logic an# compare instructions

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ubtraction

ubtraction uses 4Hs complement

In PIC18' !our instructions are available

!or subtraction%

Instructions 7unction

subl B >&(G < B ; >&(G

sub! !ile&eg' #' a ubtract >&(G !rom!ile&eg

sub!b !ile&eg' #' a ubtract >&(G !rom!ile&eg ith orro

sub!b !ile&eg' #' a ubtract !ile&eg !rom>&(G ith orro

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ubtraction !or unsigne# numbers

e.g.'mo$lw 0x2.

su+lw 0x.F

37 11 1111 11 1111; 43 1 11 111 111 24Hs complement

1C 1 1 11

&ule% C < 1' orro < .

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ubtraction !or unsigne# numbers

/o about this% C;5(J

i.e.'mo$lw 0x*'

su+lw 0x/C

"he anser is rong. >hyJ

ou have a borro 2C


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e.g.' Compute C @ 5( by using the sub!instruction.

1%e& equ 0x20

mo$lw 0x/C

mo$wf 1%e&,A

mo$lw 0x*'

su+wf 1%e&, W,A

ubtraction using sub!

C 1 11; 5( 11 1 24Hs comp *( 111 111

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Multibyte ubtraction% sub!b

ubtract 4616 by 1777 2he$ *o the L subtraction

16 < 1 11

;77 ;D 4Hs complement < 1

L &esult < 1 11

)ote C < ' orro < 1

*o the M subtraction

46 < 1 11

;17 ;D 4Hs complement < 111 1

&esult < 11 ince e orro < 1 in L subtraction

M &esult < 11

)ote C < 1' orro <

7inal &esult < 6 1528


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Multibyte ubtraction% sub!b

4616 @ 1777

Assembly Co#e Pseu#oco#e

movlw 0xFF

sublw 0x15 [WREG] = 15-FF

movwf FirstReg, A [FirstReg] = [WREG] (orrow=1!

movlw 0x"5

movwf #e$o%&Reg, A

movlw 0x1F

subwfb #e$o%&Reg, F, A [#e$o%&Reg] = "5-1F-orrow

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&epresentation o! igne# )umber

igne# 8;bit representation% *9 2M represents sign % 1 i! negative' i!

positive

*;*5 represent the magnitu#e o! the number.

Positive number same as the unsigne# number representation

ranges !rom to 49;1 because 9 bits are use#

)egative number% 4Hs complement >rite the magnitu#e o! the number as a unsigne#

8;bit number

Invert each bit

A## 1 to it 30


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8;bit igne# )umber &epresentation

*ecimal inary /e$+127 0111 1111 7F

..... ..... .....

+2 0000 0010 02

+1 0000 0001 01

0 0000 0000 00

-1 1111 1111 FF

-2 1111 1110 FE.... .... ....

-127 1000 0001 81

-128 1000 0000 8031


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($ample

32

e.g.'mo$lw 0x2

addlw 0x22

;145 1 1 24Hs comp 111 111 3 1 1

;K4 11 1 24Hs comp 11 11

7lags in "A", register ill be set as% ) < 1 2*9 < 1 O? < 2)o over!lo. &esult is correct.

&ule% )egative number Positive number O?<


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Over!lo problem in signe# operations

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e.g.'mo$lw 345*4

addlw 34604

K5 11 9 1 11

;K 11 11

7lags in "A", register ill be set as% ) < 1 2*9 < 1 O? < 1

um < ;K


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Anser the !olloing -uestions%

ho the status o! the ) an# O? !lag bits!or the !olloing co#e%

2a movl $59

a##l $KK

2b movl $

a##l $5

2c movl $65

a##l $87

2# movl $77 a##l $74

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inary Co#e# *ecimal 2C* ystem

All a##itions are per!orme# in binary!ormat in PIC18 MC,

*ecimal numbers can be enco#e# in

binary;co#e# #ecimal 2C* !ormat

C* #ecimal C* #ecimal

11 6

1 1 11 51 4 111 9

11 3 1 8

1 11 K

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C* A##ition

inary a##ition o! C* numbers oul# notbe correct i! one o! the !olloing occurs%1. I! a sum #igit is greater than K

e.g.' 4 35 66

59 9 99

8 9* CC

4. I! a sum #igit has a carry o! 1 to the higher #igit

e.g.' 4K 9

9

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C* A##ition

olution% A## $5 to these to types o!sum #igits.

e.g.' 4 35 66 4K

59 9 99 98 9* CC 9

5 5 55 5

K1 83 134 95

dawoul# #o this !or you. mo$f 0x-0, W, A

addwf 0x-/, W, A

daw 37


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#a Instruction

#a instruction a##s $5 to the upperor loer byte i! necessary.

#a instruction or0s only on >&(G

Loer nibble% I! the loer nibble 2 bitsis greater than K or i! *C < 1' a## $5

to the loer nibble.

,pper nibble% I! the higher nibble 2 bitsis greater than K or i! C < 1' a## $5 to

the upper nibble.38


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($ample% C* A##ition o! 3 numbers

e.g.' 7in# the sum o! the values $88' $5K an# $K9. Put the sumin !ile register $6 an# $5.

78+1te equ 0x0*

98+1te equ 0x0"

or& 0x00

clrf 78+1te clrf 98+1te

mo$lw 0x

addlw 0x*5

daw

+nc 8-

incf 78+1te, F, A8-: addlw 056

daw

+nc O$er

incf 78+1te, F,A

O$er:mo$wf 98+1te,A

end 39


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Multiplication

PIC18 has to instructions !or 8;bitmultiplication% mul! ! an# mull 0.

"he pro#ucts are store# in the

P&O*/%P&O*L register pair. "he !olloing instruction se-uence

per!orms 8;bit multiplication operation%

mo$f 0x-0,W,Amulwf 0x--,A

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Logic Instructions

PIC18 provi#es instructions to per!ormlogic operations such as A)*' O&'

($clusive;O& an# complement.


andlw K A)* B ith >

andwf fileReg d a A)* > ith !ile&eg

io!lw K Or B ith >

io!wf fileReg d a Or > ith !ile&egxo!lw K ($clusive Or B ith >

xo!wf fileReg d a ($clusive Or > ith !ile&eg

co"f fileReg d a Complement !ile&eg

negf fileReg a Pro#uce 4Hs complement o! !ile&eg41


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Compare instructions

Compare instructions compare a valuein the !ile register ith the contents o!

the >&(G register.

"hree instructions !or compareoperations%


c#f$g% fileReg a Compare ! ith >&(G' s0ip i! !ile&eg D >&(G

c#f$e& fileReg a Compare ! ith >&(G' s0ip i! !ile&eg < >&(G

c#f$l% fileReg a Compare ! ith >&(G' s0ip i! !ile&eg >&(G

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($ample% cp!slt

e.g. >rite a program to !in# the greater o! the

?AL1 an# ?AL4 registers an# place it in !ile

register location $4.

1%e& equ 0x20

A98- equ 0x00

A982 equ 0x0-

mo$f A98-, W, A

cpfslt A982, A

mo$f A982, W, A

mo$wf 1%e&, A 43


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($ample

e.g.' uppose a value " is store# in the

register $4. Put a value to the

register $41 accor#ing to the

!olloing scheme%I! " < 96' then E$41F < 1

I! " D 96' then E$41F < 4

I! " 96' then E$41F <

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($ample

File%e& equ 0x20%esult equ 0x2-

ain: mo$lw 3


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3.3 Looping an# ranching

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Looping in PIC

Loop @ repeating a se-uence o! instructionsa certain number o! times.

e.g.' "o a## 3 to >&(G !ive times' I coul# #o%mo$lw 0x00

addlw 0x0.

addlw 0x0.

addlw 0x0.

addlw 0x0.

addlw 0x0.

*isa#vantage% "oo much co#e space is

nee#e# i! repeating 1 times ,se looping

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Looping using #ec!s instruction

#ec!s stan#s !or *(Crement !ileregister an# 0ip i! Nero.

7ormat% decfs> f, d

here fis the 8;bit a##ress o! the !ileregister an# # in#icates the #estination o!

#ecremente# value% > @ >&(G' 7 @ 7ile

&egister

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Looping using #ec!s instruction

e.g.' >rite a program to 2a initialie >&(G to 2ba## $6 ten times to >&(G an# put the result in

the P&O*L register

count equ 0x00

mo$lw d?-04

mo$wf count, A

mo$lw 0x00

Addore:addlw 0x0"

decfs> count, F, A

&oto Addore

mo$wf @%O39

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Looping using bn instruction

bn stan#s !or branch i! the N !lag in thestatus register is ero

7ormat% bn label

e.g.' Implement the loop in the last sli#eusing bn.

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Comparison beteen #ec!s an# bn

#ec!scount equ 0x00

mo$lw d?-04

mo$wf count, A

mo$lw 0x00

Addore:addlw 0x0"

decfs> count, F, A

&oto Addoremo$wf @%O39

bncount equ 0x00

mo$lw d?-04

mo$wf count, A

mo$lw 0x00

Addore: addlw

0x0"

decf count, F, A

+n> Addore

mo$wf @%O39

51

O h #i i l


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Other con#itional umps

"hese branching instructions umpshen C an# N in the "A", register are

1 or

bn% ump i! N < 2previously #escribe# b% ump i! N < 1

bnc% ump i! C <

bc% ump i! C < 1

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( l ! b # N


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($amples o! umps base# on N

e.g.' >rite a program to #eterminehether !ile register $3 contains a value

other than $. I! not' put $ in it.

file%e& equ 0x.0

mo$f file%e&, F

+> ext

mo$lw 0x00mo$wf file%e&

ext: ###

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( l ! b # C


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($amples o! umps base# on C

e.g.' 7in# the sum o! the values $9K' $76 an# $(4. Putthe sum in !ile register $6 an# $5.

78+1te equ 0x0*

98+1te equ 0x0"

or& 0x0000 clrf 78+1te

clrf 98+1te

mo$lw 0x65

addlw 0xF"

+nc 8- incf 78+1te, F

8-: addlw 0'2

+nc O$er

incf 78+1te, F

O$er:mo$wf 98+1te

end54

h t


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hort umps

"he instruction+nc la+elis interprete# as+nc n by theassembler' here n is a signe# 1;byte number ithin ;148 to

149.

nis the relative a##ress o! the branching #estination ith

respect to the current PC. n is e$presse# in number o!

instructions 2i.e.' relative a##ress < 4n i! e$presse# in a##ress

ecause the target must be ithin 465 instructions o!

the current PC' con#itional branches are short "umps.55

P M ! th b ( l


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Program Memory o! the bnc ($ample

"he label )1 is one instruction aay 2at

8 !rom the current PC 25 hen

branching occurs. Opco#e < (31ump 1 instruction 2or 4

bytes !rom 5 to 8 i! branching

occurs. 56

L


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Long umps

gotospeci!ies the absolute a##ress o!the branching #estination an# can ump

to anyhere in the program memory.

goto is a ;byte instruction.

57

( l ! b t i t ti GO"O


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($ample o! a ;byte instruction% GO"O

>hy ;byteJ "he machine co#e must

contain the a##ress o! the

#estination in the program

memory 241;bit Only the most signi!icant

4 bits are inclu#e#. >hyJ Program memory

are organie# as4;byte bloc0s. L

must be .

58

M hi # ! GO"O


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Machine co#e o! GO"O

"he goto Main line in our previouse$ample !orces PC to $' here

the Main label is.

"he machine co#e is

'F02

F000

"hus' the program goes to

1 in binary

2i.e.' $ in he$59

( l ! th t i t ti


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($ample !or the goto instruction

e.g.' In our program' e ant to branchto a##ress $4. >hat is the

machine co#e o! the goto instructionJ

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Long umps

bra allocate# 11 bits !or storing the relative

a##ress o! the targeting instruction.

bra can ump !orar# !or a ma$. o! 143instructions an# bac0ar# !or a ma$. o!

14 instructions.

61

( ercise on bra a##ress enco#ing


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($ercise on bra a##ress enco#ing

62

'alc(la%e %)e !ela%i*e add!e$$e$ "a!,ed / encoded in %)e

o#code $)own elow.

Comparison among 3 types o!


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p g yp

branching instructions

Con#itionalranching ,ncon#itional ranching

+c, +nc, +>, +n>,+n, +nn, +o$, +no$ +ra &oto

!anc) acco!ding %o %)ew)e%)e! a flag in %)e55 !egi$%e!ed i$!ai$ed.

!anc) (ncondi%ionall

5)e o#e!and of %)e$e in$%!(c%ion$ $#ecifie$ %)eadd!e$$ of %)e de$%ina%ion of %)e ("# !ela%i*e %o %)e#o$i%ion of %)e nex% in$%!(c%ion

5)e o#e!and of go%o$#ecifie$ %)e a$ol(%eadd!e$$ of %)e

de$%ina%ionle %o ("# -128 %o+127 line$ wi%) !e$#ec% %oc(!!en% in$%!(c%ion

le %o ("# -1024 %o+1023 line$ wi%) !e$#ec%%o c(!!en% in$%!(c%ion

le %o ("# %o anw)e!ein %)e #!og!a" "e"o!

63

($ercise on &elative=Absolute A##resses


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($ercise on &elative=Absolute A##resses

&OM Machine LI)( O,&C(A##ress Co#e

44 CLOCB $4 43 inary 4 "ens 46 ,nits 45 ()*C 49

48 O&G $ (7JJ 7JJJ 4K goto Main 3 O&G $44 (* 31 Main% movl #Q99Q44 5(4 34 mov! inary' A4 5A41 33 in4C*% clr! "ens' A

45 5A44 3 clr! ,nits' A48 64 36 mov! inary' >' A4A 775 35 Loop% a##l ;#Q1Q4C (3JJ 39 bnc )e$t4( 4A41 38 inc! "ens' 7' A3 *JJJ 3K bra Loop34 7A )e$t% a##l #Q1Q3 5(44 1 mov! ,nits' A 4 ()*

64

'alc(la%e %)e !ela%i*e9a$ol(%e add!e$$e$ "a!,ed /

encoded in %)e o#code $)own in :ine$ 2; 37 3; in %)e following#!og!a".

ranch=ubroutine Instruction "iming


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ranch instructions are those that changethe program counter 2PC 2i.e.' all

branching an# call instructions

ince the !etch stage incorrectly gets themachine co#e !or the ne$t se-uential

instruction hen branching' this machine

co#e must be #umpe#.

65

bra Instruction in *ata heet


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bra Instruction in *ata heet

,ncon#itionalbranch

Pre;!etche#

instruction must be

#umpe#.

)othing can be

e$ecute# in the

secon# cycle

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"his #umping results in ta0en branches2inclu#ing uncon#itional branches

re-uiring to instruction cloc0s to

process. ranches that are not ta0en re-uire only

one machine cycle.

67

N as #escribe# in *ata heet


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N as #escribe# in *ata heet

I! ump' instructionis !etche# incorrectly

an# must be

#umpe#.

)othing can be

e$ecute# in the

secon# cycle.

68

,sing Program Loops to Create "ime *elays


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Consi#er the !olloing co#e !ragment%3ela19oop:decfs> 3'9A89

+ra 3ela19oop

ecause the *(LAL register is 8;bit'

the loop can be repeate# a ma$imum o!

465 times.

/o #o e get a longer #elayJ

olution% Looping ithin a loop or

#ested Loop

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3ela19oop:decfs> 3'9A89 +ra 3ela19oop

decfs> 3'9A87

+ra 3ela19oop e.g.' *(LAL < $' *(LA/ < $4

"he !irst #ec!s instruction ill e$ecute !or 465 times.

*(LAL ill become a!ter the 465th#ecrement. "he bra line ill be s0ippe#.

*(LA/ ill be #ecremente# to 1. )ot ero. ranch bac0 to the start.

"he !irst #ec!s instruction ill e$ecute !or 465 times.

*(LA/ ill be #ecremente# to . (n# program.

In total' the !irst #ec!s instruction e$ecutes 4$465 times.

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"he PIC18 uses a crystal oscillator togenerate the cloc0 signal nee#e# to

control its operation.

"he instruction e$ecution time ismeasure# by using the instruction cycle

cloc0.

1 instruction cycle < cloc0 cycles.

A #esire# time #elay is create# by

repeating a certain set o! instructions

using loops.71

PIC Multistage ($ecution Pipeline


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PIC Multistage ($ecution Pipeline

($ecution ta0es cloc0 perio#s o! theoscillator.

e.g.' Cloc0 cycle < M/: Instruction cycle 3'9A89 1 instruction cycle 24 i! s0ip+ra 3ela19oop 4 instruction cycles

decfs> 3'9A87 1 instruction cycle 24 i! s0ip

+ra 3ela19oop 4 instruction cycles

74

ou shoul# be able to


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ou shoul# be able to .....

Co#e PIC assembly language instructions to createloops.

Co#e PIC assembly language con#itional branch

instructions.

($plain ho status bits a!!ect the behaviour o!con#itional branch instructions.

Compare the properties o! long ump an# short ump

instructions.

Co#e long ump instructions !or uncon#itional ump. Calculate the target a##resses !or con#itional

branch instructions.

($plain in hat situation neste# loop is re-uire# in

chapter 3a pic18 assemblylanguageprogrammingparta(2)

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