Assemblyy Language
g g Programming
g
g
Hsiao-Lung
H
i L
Chan
Ch
Dept Electrical Engineering
Chang Gung University, Taiwan
chanhl@mail cgu edu tw
[email protected]
Elements of an assemblyy language
g g statement




Label
Mnemonics
Operands
Comment
2
Label field

Valid labels
loop
g
_again
c?gtm

addwf
addlw
andlw
0x20,F,A
0x03
0x7F
Invalid labels
30r5
clrf
three-four cpfsgt
isbig
btfsc
0x16,A
0x14,A
0x15,0x07,B
3
Mnemonic field


Either an assembly instruction mnemonic or an assembler
directive
(comment)
Example
p
false
loop:
equ
goto
incf
0
; equ is assembler directive
start
0x20,W,A
4
Operand
p
field

Operands for instructions or arguments for assembler
directives
true
cpfseq
equ
movff
0x20,A
1
0x30,0x65
5
Assembler directives


Most tell the assembler to do something other than
creating the machine code
Assembler Directives





Control directives
Data directives
Listing directives
Macro directives
Object file directives
6
Control directives

The directives for conditional assembly
if <expr>
else
Endif

Example
if version
movlw
movwf
else
movlw
movwf
endif
dif
== 100 ; check current version
0x0a
io_1,A
0x1a
io_2,A
7
Control directives (cont.)
(
)

The directive declares the beginning of a section of
program code
[<label>] code [<ROM address>]
 Example
reset

code
goto
0x00
start
The directive indicates the end of the program
end
8
Control directives (cont.)
(
)

The directive defines a text substitution string
#define <name> [<string>]
 Example
#define
length
30
#define
config
0x17,7,A
#define
sum3(x y z)
sum3(x,y,z)
(x + y + z)
.
.
test dw sum3(1,length,200) ; place 1+20+200 here
bsf config
; set bit 7 of register 0x17 to 1
9
Control directives (cont.)
(
)
ifdef <label>
 Example
#define
test_val
2
.
.
ifdef test_val
<execute test code>
endif
10
Control directives (cont.)
(
)
#undefine <label>
ifndef <label>
 Example
#define
; deletes a substitution string
led_port
1
.
.
#undefine
led_port
.
.
ifndef led_port
<execute code>
endif
11
Control directives (cont.)
(
)

The directive includes additional source file
#include “<include_file>”
((or #include <include_file>)
_
)
 Search order if on fully qualified path is specified:
current working directory, source file directory, MPASM
executable
bl directory
di


Example
#include <p18F8680.inc>
<p18F8680 inc>
; include p18F8680.inc from the installation directory of mplab.
#include “lcd_util.asm”
_
; include lcd_util.asm file from current working directory
12
Control directives (cont.)
(
)

The directive sets the default radix for data expression
radix <default_radix>
Valid radix values are: hex,, dec,, or oct
 Example
radix
dec
13
Control directives (cont.)
(
)
while <expr>
endw
 The lines between while and endw are assembled as
long as <expr> is true
 Example
p
test_mac macro chk_cnt
variable i
i 0
i=0
while i<chk_cnt
movlw i
i+=1
endw
endm
start
test_mac 6
end
14
Data directives: db, dw, dt

Reserves program memory words
db: define a data of one byte
dw: define data of one word
dt: define table

Example
led_pat
msg1
array
msg2
results
db
db
db
dw
dw
dt
0x30,0x80,0x6D,0x08
‘b’, 0x22, ’\n’
“Please
“ l
enter your choice
h
(1/2):”,0
( /2) ”
0x1234,0x2300,0x40,0x33
“The
The humidity is “,0
0
1,2,3,4,5 ;generates a series of retlw instructions
15
Data directives: equ,
q set, variable




equ: define a assembly constant
set: define an assembler variable
variable: define symbols for assembler
Example
true
false
length
width
length
equ
q
equ
set
set
set
variable
variable
1
0
0x20
0x10
0x30
; altered by other set directive
i
k=0, m, p=2
16
Macro directive



Instructions are grouped together and assigned a name
By entering the macro name, the same group of
instructions can be duplicated
p
in anyy p
place of the
program
User program is made more readable by using macros
17
Macro example
p

Define a macro
; WREG  [arg1]+[arg2]+[arg3]
sum of 3
sum_of_3
macro
arg1, arg2, arg3
movf
arg1,W,A
addwf
arg2 W A
arg2,W,A
addwf
arg3,W,A
endm

Invoke the macro
sum_of_3
f 3
0
0x20,0x21,0x22
20 0 21 0 22
18
Macro directive: exitm


Force immediate return fro the macro
Example
test
macro arg1
g
if arg1 == 3
exitm
else
error “bad file assignment”
endif
endm
19
Macro directive: local


Avoid conflict with another label declared outside the
macro
Example
p
len
width
abc
len
label
l
len
equ
equ
macro
local
set
res
set
endm
5
8
width
len,width
width
len
; allocate 8-byte memory
l 10
len-10
20
Listing
g directives

Control the MPASM listing file format



list: turn on the listing file output if it had been previously
turned off
nolist: turn off the listing file output
title: establish a text at the top of each page of the listing file
title “Prime number generator, rev 2.0”



error: issue an error message
messg: create user defined message
space: insert blank lines into the listing file
space 3

page: insert a page eject into the listing file
21
Object
j
file directoryy


Control the generation of object code
processor <processor type>
processor p18F8680
p
p


; set processor
p
type
yp to PIC18F8680
code: begin executable code section
[[<label>]] org
g <expr>
p

set subsequent code at the defined address
reset
start
org 0x00
…
goto start
org 0x100
…
22
Object
j
file directory:
y udata
Declare the beginning of uninitialized data
[<label>] udata [<RAM address>]

var1
var2
udata
res
1
res
2
; starting address is assigned at the link time
23
Object
j
file directory:
y banksel
banksel <label>
 An instruction to the linker to generate movlb k to set
active bank to the bank containing
g <label>
 Example
var1
vark
udata
res
1
…
res
1
…
code
…
banksel var1
…
banksel vark
24
Assemblyy p
program
g
template
p
org
g
goto
org
…
retfie
org 0x18
…
retfie
start …
…
end
d
0x0000 ; p
program
g
starting
g address after p
power on reset
start
0x08
; high-priority
h h
interrupt service routine
; return
; low-priority interrupt service routine
; return
; your program
25
Write a program that adds the three numbers stored in data
registers at 0x20, 0x30, and 0x40 and places the sum in data
register at 0x50
#include <p18F8720.inc> ; can be other processor
org
0x00
goto
start
org
0x08
retfie
org
0x18
retfie
start
movf
0x20,W,A
; WREG  [0x20]
addwf
0x30,W,A
; WREG  [0x20] + [0x30]
addwf
0x40,W,A
; WREG  [0x20] + [0x30] + [0x40]
movwf 0x50,A
; 0x50  sum (in WREG)
end
d
26
Byte
y order issue


Big endian: stores the most significant byte at the lowest
Big-endian:
address and stores the least significant byte in the highest
address.
Little-endian: stores the most significant byte of the
number at the highest
g
address and stores the least
significant byte of the number in the lowest address.
27
Write a program to add two 24-bit numbers stored at
0x10~0x12 and 0x13~0x15 and leave the sum at 0x20..0x22
0x20 0x22
#include <p18F8720.inc>
org
0x00
goto
start
org
0x08
retfie
org
0x18
retfie
start
movf
0x10,W,A
; WREG  [0x10]
addwf
0x13,W,A
; WREG  [0x13] + [0x10]
movwf
0x20 A
0x20,A
; 0x20  [0x10] + [0x13]
movf
0x11,W,A
; WREG  [0x11]
addwfc
0x14,W,A
; WREG  [0x11] + [0x14] + C flag
movwf
0x21,A
; 0x21  [WREG]
movf
0x12,W,A
; WREG  [0x12]
addwfc
0x15,W,A
; WREG  [0x12] + [0x15] + C flag
movwf
end
0x22,A
; 0x22  [WREG]
28
Write a program to subtract 5 from memory locations 0x10
to 0x13
start
#include <p18F8720.inc>
p
org
0x00
goto
start
org
0x08
retfie
org
0x18
retfie
movlw 0x05
; WREG  0x05
subwf 0x10,F,A
; 0x10  [0x10] – 0x05
subwf 0x11,F,A
; 0x11  [0x11] – 0x05
subwf
b f 0x12,F,A
0 12 F A
; 0x12
0 12  [0x12]
[0 12] – 0x05
0 05
subwf 0x13,F,A
; 0x13  [0x13] – 0x05
end
29
Write a program that subtracts the number stored at
0x20..0x23 from the number stored at 0x10..0x13 and leaves
the difference at 0x30..0x33
start
#include
org
goto
org
retfie
org
retfie
movf
subwf
movwf
movf
subwfb
b fb
movwf
movf
subwfb
movwf
movf
subwfb
movwf
end
<p18F8720.inc>
0x00
start
0x08
0x18
0x20,
0x10,
0x30,
0x21,
0 11
0x11,
0x31,
0x22,
0x12
0x12,
0x32,
0x23,
0x13,
0x33,
W,
W,
A
W,
W,
W
A
W,
W,
W
A
W,
W,
A
A
A
; 0x30  [0x10] – [0x20]
A
A
; 0x31  [0x11] – [0x21]
A
A
; 0x32  [0x12] – [0x22]
A
A
; 0x33  [0x13] – [0x23]
30
Binaryy coded decimal ((BCD)) addition


Decimal digits are encoded using 4 bits
Let data register 0x24 and 0x25 holds BCD numbers, add
these two BCD numbers and save the sum in 0x30
movf
0x24,W,A
addwf
0x25,W,A
daw
movwf
; adjust
j
for valid BCD
0x30,A
31
BCD addition


h31
h24
h36
h29
+ h47
+ h67
+ h47
+ h47
h78
h8B
h7D
h70
daw
 Add 0x6 to every sum digit greater than 9
 Add 0x6 to every sum digit that produce a carry
h31
h24
h36
h29
+ h47
+ h67
+ h47
+ h47
h78
h8B
h7D
h70
+h6
+h 6
+h6
h91
h83
h76
Digital carry (DC) in status register indicate there is a carry from bit 3
to b
bitt 4
32
Write an instruction sequence that adds the decimal numbers
stored at 0x10...0x13 and 0x14...0x17 and stores the sum in
0x20..0x23
start
#include
…
movf
addwf
daw
movwf
movf
addwfc
daw
movwf
movf
addwfc
dd f
daw
movwf
movf
addwfc
daw
movwf
end
<p18F8720.inc>
0x10,W
0x14,W
0x20
0x11
0x15,W
; add the least significant byte
; adjust for valid BCD
; save in the destination
; add the second to least significant byte
0x21
0x12
0 16
0x16
; add the second to most significant byte
0x22
0x13
0x17
; add the most significant byte
0x23
33
Multiplication
p

8-bit
8
bit multiplication instruction
mulwf f
mullw k

Example
movf
mulwf
movff
movff
0x10,W,A
0x11,A
PRODH,0x21 ; upper byte of the product
PRODL,0x20 ; lower byte of the product
34
16-bit multiplication
p
P = PH P L Q = Q H Q L
35
16-bit multiplication:
multiply two numbers at N1:N1+1 and M1:M1+1
n1_h
n1_l
m1_h
m1_l
M1
N1
PR
#include <p18F8720.inc>
p
equ
0x37 ; first number
equ
0x23
equ
0x66 ; second number
equ
0x45
set
0x00 ; multiplicand
set
0X02 ; multiplier
set
0x06 ; product
org
0X00
goto
start
org
0 08
0x08
retfie
org
0x18
retfie
36
16-bit multiplication
p
(cont.)
(
)
start
movlw
movwf
movlw
movwf
movlw
movwf
movlw
movwf
m1_h
M1+1,A
m1_l
M1,A
n1_h
N1+1 A
N1+1,A
n1_l
N1,A
; set up
p M1+1:M1
movf
mulwf
l f
movff
movff
M1+1,W,A ; compute M1H  N1H
N1 1 A
N1+1,A
PRODL,PR+2
PRODH PR+3
PRODH,PR+3
; set up N1+1:N1
37
16-bit multiplication
p
(cont.)
(
)
movf
mulwf
movff
movff
M1,W,A
; compute M1L  N1L
N1,A
PRODL,PR
PRODH PR+1
PRODH,PR+1
movf
mulwf
movf
addwf
movf
addwfc
movlw
addwfc
M1,W,A
N1+1,A
PRODL,W,A
PR+1,F,A
, ,
PRODH,W,A
PR+2,F,A
0
PR+3,F,A
; compute M1L  N1H
; add M1L  N1H to PR
; add carry
38
16-bit multiplication
p
(cont.)
(
)
movf
mulwf
movf
addwf
movf
addwfc
movlw
addwfc
nop
p
end
M1+1,W,A
; compute M1H  N1L
N1,A
PRODL,W,A ; add M1H  N1L to PR
PR+1 F A
PR+1,F,A
PRODH,W,A
PR+2,F,A
0
PR+3,F,A
; add carry
39
PIC18 memoryy access
Inside the 
c chipp
up to 2 MB of
program memory
4096 registers
Program
P
Memory
Space
(a portion
of this
space is on
the c
chip)
21-bit progam address
Program
counter
(PC)
12-bit register address
PIC18
CPU
16-bit instruction bus
8-bit data bus
Data
Memory
Space
(Special
function
registers and
general
purpose
RAM))
Fi
Figure
1.3
1 3 The
Th PIC18 memory spaces
40
Instructions for changing program counter:
goto vs.
vs bra

Jump
p to absolute address




goto k
32-bit instruction: 1110 1111 kkkk kkkk
1111 kkkk kkkk kkkk
jump to address represented by k
Jump to relative address



BRA n ; n is branch offset
16-bit instruction: 1110 0nnn nnnn nnnn
jump to the instruction with address equals to PC+2+n



forward branch: bra 10
backward branch: bra -10
Use label to replace branch offset
loop …
…
bra loop
41
Conditional branch vs. unconditional branch

Unconditional branch


BRA n
Conditional branch



BCC n:
jump to the instruction with address equals to PC+2+n if the condition code CC is
true
CC can be anyy one of the following:
g
C:
N:
NN:
NOV:
NZ:
OV:
Z:
C flag is set to 1
N flag is set to 1 which indicates that the previous operation result was negative
N flag is 0 which indicates non-negative condition
V flag is 0 which indicates there is no overflow condition
Z flag is 0 which indicates the previous operation result was not zero
V flag is 1 which indicates the previous operation caused an overflow
Z flag is 1 which indicates the previous operation result was zero
42
Alternative conditional branch
cpfseq
p q
cpfsgt
cpfslt
decfsz
dcfsnz
incfsz
infsnz
tstfsz
btfsc
btfss
f,a
,
f,a
f,a
f,d,a
f,d,a
fda
f,d,a
f,d,a
f,a
f,b,a
f,b,a
;
;
;
;
;
;
;
;
;
;
compare
p
register
g
f with WREG,, skip
p if equal
q
compare register f with WREG, skip if equal
compare register f with WREG, skip if less than
decrement f, skip if 0
decrement f, skip if not 0
increment ff, skip if 0
increment f, skip if not 0
test f, skip if 0
test bit b of register f, skip if clear
test bit b of register f, skip if set
43
Example
p
n
equ
q
lp_cnt set
…
movlw
movwf
loop …
…
decfsz
goto
20
0x10
n
lp_cnt
; n has the value of 20
; assign file register 0x10 to lp_cnt
; prepare to repeat the loop for n times
; program loop
lp_cnt,F,A ; decrement lp_cnt and skip if equal to 0
loop
; executed if lp_cnt  0
decf
bnz
lp_cnt,F,A ; decrement lp_cnt
loop
; executed if lp_cnt  0
44
Write a program to compute 1 + 2 + 3 + … + n and
save the sum at 0x00 and 0x01
sum=0;
for (i = 1; i<=n; i++)
sum += i;;
45
compute
p
1 + 2 + 3 + … + n (cont.)
(
)
#include <p18F8720.inc>
n
equ
D'50'
sum_hi set
0x01
; high byte of sum
sum lo set
sum_lo
0x00
; low byte of sum
i
set
0x02
; loop index i
org
0x00
; reset vector
goto
start
org
0x08
retfie
org
0x18
retfie
46
compute
p
1 + 2 + 3 + … + n (cont.)
(
)
start
clrf
clrf
clrf
incf
sum_lp movlw
cpfsgt
bra
bra
p
movf
add_lp
addwf
movlw
addwfc
incf
bra
exit_sum nop
end
sum_hi,A
sum_lo,A
i,A
iFA
i,F,A
n
i,A
add_lp
exit_sum
i,W,A
, ,
sum_lo,F,A
0
sum hi F A
sum_hi,F,A
i,F,A
sum_lp
; initialize sum to 0
;
;
;
;
;
;
;
;
initialize i to 0
i starts from 1
place n in WREG
compare i with n and skip if i > n
perform addition when i  50
it is done when i > 50
place
p
i in WREG
add i to sum_lo
; add carry to sum_hi
sum hi
; increment loop index i by 1
47
Find the largest element stored in the array that is
stored in data memory locations from 0x10 to 0x5F
arr_max=arr[0];
[0]
for (i=1; i<n; i++)
if (arr[i]>arr_max)
arr_max=arr[i];
48
Find the largest
g
element (cont.)
(
)
arr_max
i
n
start
equ
q
equ
equ
#include
org
goto
org
retfie
org
retfie
movff
ff
lfsr
clrf
0x00
0x01
D'80' ; the array count
<p18F8720.inc>
0x00
start
0x08
0x18
0x10,arr_max
0
10
; set arr[0]
[0] as the
h initial
i i i l max
FSR0,0x11
; place address of arr[1] in FSR0
iA
i,A
; initialize loop count i to 0
49
Find the largest
g
element (cont.)
(
)
again
g
movlw
cpfslt
bra
movf
cpfsgt
bra
bra
replace movwf
next_i incf
goto
done nop
end
n-1
i,A
done
POSTINC0,W
arr_max,A
replace
next_i
arr_max,A
i,F,A
again
; skip if i < n-1
; all comparisons have been done
; is arr_max > arr[i]?
; no
; yes
; update the array max
50
Reading
g and writing
g data in program
p g
memoryy
Table write
(TBLWT)
Table read
(
(TBLRD)
)
51
Write an instruction sequence to read a byte from
program memory at 0x60 into TABLAT
clrf
clrf
movlw
movwf
tblrd
tblrd*
TBLPTRU,A
TBLPTRH,A
0x60
TBLPTRL,A
52
Table read and write instructions
Table 2.11 PIC18 MCU table read and write instructions
Mnemonic,
operator
TBLRD*
TBLRD*+
TBLRD*
TBLRD*TBLRD+*
TBLWT*
TBLWT*+
TBLWT
+
TBLWT*TBLWT+*
Description
Table read
Table read with post-increment
Table read with post-decrement
post decrement
Table read with pre-increment
Table write
Table write with post
post-increment
increment
Table write with post-decrement
Table write with pre-increment
16-bit instruction word
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
1000
1001
1010
1011
1100
1101
1110
1111
Status
affected
none
none
none
none
none
none
none
none
53
Reading
g the program
p g
memoryy location p
prog_loc
g
; Step 1. Place the address of prog_loc
prog loc in TBLPTR registers
movlw
upper prog_loc
movwf
TBLPTRU,A
movlw
high prog_loc
movwf
TBLPTRH A
TBLPTRH,A
movlw
low prog_loc
movwf
TBLPTRL A
TBLPTRL,A
; Step 2. Perform a TBLRD instruction.
tblrd
tblrd*
54
Logic
g instructions
55
Examples
p

To set bits 7, 6, and 0 of PORTA to 1
movlw B’11000001’
, ,
iorwf
PORTA,F,A

To clear bits 4, 2, and 1 of PORTB to 0
movlw B’11101001
andwf PORTB,F,A

To toggle bits odd bits of PORTC
movlw B’10101010’
xorwf PORTC
56
Write a program to find out the number of elements in an
array of 8-bit elements that are a multiple of 8. The array is
in the program memory
57
Number of elements of a multiple
p of 8 (cont.)
(
)
#include <p18F8720.inc>
p
ilimit equ
0x20
; loop index limit
count set
0x00
ii
set
0x01
; loop index
mask equ
0x07
; used to masked upper five bits
org
0x00
goto
start
…
; interrupt service routines
start clrf
count,A
movlw ilimit
movwff ii
; initialize
i i i li ii to ilimit
ili i
movlw upper array
movwf TBLPTRU,A
TBLPTRU A
movlw high array
movwf TBLPTRH,A
58
Number of elements of a multiple
p of 8 (cont.)
(
)
movlw low arrayy
movwf TBLPTRL,A
movlw mask
i_loop tblrd*+
; read an array element into TABLAT
andwf TABLAT,F,A
bnz
next
; branch if not a multiple of 8
incf
count,F,A
; is a multiple of 8
next decfsz ii,F,A
; decrement loop count
bra i_loop
nop
array db
0 00 0 01 0 30 0 03 0 04 0 05 0 06 0 07 0 08 0 09
0x00,0x01,0x30,0x03,0x04,0x05,0x06,0x07,0x08,0x09
db
0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,0x10,0x11,0x12,0x13
db
0x14 0x15 0x16 0x17 0x18 0x19 0x1A 0x1B 0x1C 0x1D
0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D
db
0x1E,0x1F
end
59
Using
g program
p g
loops
p to create time delays
y

A Macro to repeat an instruction for certain number of
times
dup_nop macro kk ; duplicate the nop instruction kk times
variable i
i=0
while i < kk
nop
; takes 1 instruction cycle time
i += 1
endw
endm
d
60
Write a program to create a time delay of 100 ms for the
demo board that uses a 40 MHz crystal oscillator to operate
lp_cnt1
p
lp_cnt2
loop1
loop2
equ
q
0x21
One instruction cycle = 100 ns
equ
0x22
movlw D’200’
movwf lp_cnt1,A
movlw D’250’
Produce a delay of 0.5 ms
movwf lp_cnt2,A
lp cnt2 A
dup_nop 17
; 17 instruction cycles
decfsz lp_cnt2,F,A ; 1 instruction cycle (2 when [lp_cnt1]=0)
bra
loop2
; 2 instruction cycles
decfsz lp_cnt1,F,A
b
bra
l
loop1
1
61
Rotate instructions
7
6
5
4
3
2
1
0
C
Figure 2.17 Operation performed by the rlcf f,d,a instruction
C
7
6
5
4
3
2
1
0
Figure 2.19 Operation performed by the rrcf f,d,a instruction
7
6
5
4
3
2
1
0
Figure 2.18 Operation performed by the rlncf f,d,a instruction
7 6
5 4 3
2 1 0
Figure 2.20 Operation performed by the rrncf f,d,a instruction
62
Examples
The result is
0
1
1
0
0
1
1
0
0
1
1
0
0
0
0
1
1
Original value
New value
[0x10] = 1010 1001 [0x10] = 01010010
C=0
C=1
0
Figure 2.21 Operation of the RLCF 0x10,F,A instruction
The result is
1
1
1
1
0
1
0
0
0
0
1
0
1
1
1
1
1
1
Original value
New value
[0x10] = 1100 0111 [0x10] = 1110 0011
C=1
C=1
Figure 2.22 Operation of the RRCF 0x10,F,A instruction
63
Examples
p
Th result
The
lt is
i
0
1
1
0
1
1
1
0
original value
new value
[0x10] = 0110 1110 [0x10] = 0011 0111
0
0
1
1
0
1
1
1
Figure 2.23
2 23 Operation performed by the rrncf 0x10,
0x10 F,
F A instruction
Th result
The
lt is
i
0
1
1
1
1
0
0
1
1
1
1
1
1
0
0
Before
After
[0x10] = 0110 1110
[0x10] = 1101 1100
0
Figure 2.24
2 24 Operation performed by the rlncf 0x10,
0x10 F,
F A instruction
64
Bit operation
p
instructions
bcf
bsf
btg
f, b, a
f, b, a
f, b, a
Examples
bcf STATUS,C,A
bsf sign,0,A
sign 0 A
btg sign,0,A
; clear bit b of register f
; set bit b of register f
; toggle bit b of register f
; clear the C flag of the STATUS register
; set the bit 0 of register sign to 1
; toggle bit 0 of register sign
; (0 to 1 or 1 to 0)
65
Perform multiplication
p
byy shift left operations
p

Multiply the 3
3-byte
byte number store at 0x00…0x02 by 8
p
loop
movlw
bcf
rlcf
rlcf
rlcf
decfsz
goto
0x03
STATUS,, C,, A
0x00, F, A
0x01, F, A
0x02, F, A
WREG,W,A
loop
; set loop count to 3
; clear the C flag
g
; shift left one place
; shift 3 places?
66
Perform division byy shifting
g to the right
g

Divide the 3
3-byte
byte number stored at 0x10…0x12 by 16
p
loop
movlw
bcf
rrcf
rrcf
rrcf
decfsz
goto
0x04
STATUS,, C,,
0x12, F, A
0x11, F, A
0x10, F, A
WREG,W,A
loop
; set loop count to 4
A
; shift right 1 place
; shifted right 4 places?
67
Reference

Han Way Huang, PIC Microcontroller: An Introduction to
Han-Way
Software and Hardware Interfacing, Thomson Delmar
Learning, 2005.
68