Ch 3
Objectives
CMPE328 Microprocessors
„
(Spring 2007-08)
„
ALU Instructions and Programs
„
„
By Dr. Mehmet Bodur
„
„
The 8-bit and 16-bit, signed and unsigned addition, and
subtraction operations.
Conversion between ASCII, packed BCD, unpacked
BCD and binary number formats
Effect of arithmetic instruction on the flag register
Coding of Arithmetic Instructions NEG, ADD, ADC, SUB,
SBB, MUL and DIV, and CMP; decimal arithmetic
corrections DAA, DAS; ASCII arithmetic corrections
AAA, AAS, AAM, and AAD.
Coding of Logic Instructions AND, OR, XOR; shift and
rotates SHR, SHL, ROR, ROL, RCR, RCL.
Bitwise manipulations using C language.
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
Section 3.1
Section 3.1
Signed and Unsigned Numbers
Sign Extension
„
„
8-bit signed number can
describe numbers
from –128 to + 127.
„
(80 81 … FF 00 01 … 7F)
„
16-bit signed number can
describe
from –32768 to +32767.
„
(8000 … FFFF 0000 0001 … 7FFF )
„
Signed addition may yield
overflow error
CMPE328 Spring 2007-08
„
8-bit unsigned number
can describe numbers
from 0 to + 255.
(00 …. FF)
16-bit unsigned number
can describe
from 0 to +65535
(0000 0001 … FFFF)
Unsigned addition may
yield carry flag as an
extra bit.
Dr.Mehmet Bodur, EMU-CMPE
2
„
„
„
3
CBW
(8086/80386 instruction)
Extends the sign of AL over AX.
Example:
AL= 24h (=36) ;
after CBW, AX= 0024h (=36)
AL= B0h (= – 80);
after CBW, AX=FFB0h (= – 80)
CWD
(8086/80386 instruction)
Extends the sign of AX over DX.
AX=9208h, after CWD DX=FFFFh, AX=9208h
MOVSX dst, src
(80386 instruction)
Moves from source to destination with sign extension.
dst is 16-bit, src is 8-bit. (for signed extension)
MOVZX dst, src
(80386 instruction)
Moves from source to destination with zero extension.
dst is 16-bit, src is 8-bit. (for unsigned extension)
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
4
Section 3.1
Section 3.1
ADD Instruction
„
add d8, s8
„
„
„
„
„
„
s8 : al,bl,cl,dl,ah,bh,ch,dh or constant
d8 : al,bl,cl,dl,ah,bh,ch,dh
add d16, s16
s16 : ax,bx,cx,dx,si,di,sp,bp or constant
d16 : ax,bx,cx,dx,si,di,sp,bp, cs,ds,es,ss
(cs,ds,es,ss cannot be used with a constant s16)
add d, [const] ; dest ←dest+ mem[DS:const]
add d, [r] ; dest ←dest + mem[DS:r]
r : bx,di,si ; d : d8 or d16
Restrictions: d cannot be a memory location.
Flags affected are: CSPAZO;
Operands can be both signed or unsigned.
Dr.Mehmet Bodur, EMU-CMPE
CMPE328 Spring 2007-08
Adding Multiple Words
5
LSB
words
added by
ADD,
all other
words
added by
ADC, to
propagate
the carry.
CMPE328 Spring 2007-08
.MODEL SMALL
.STACK 64
.DATA
num1 dd 12345678h
num2 dd 13579BDFh
SUM dd ?
.CODE
MAIN PROC FAR
;program entry point
MOV AX,@DATA ;data segment
MOV DS,AX
; goes into DS
MOV AH,4CH ;Exit to DOS
INT 21H
MAIN ENDP
END MAIN
Dr.Mehmet Bodur, EMU-CMPE
TITLE
PROG3-2 (EXE) MULTIWORD ADDITION
.MODEL SMALL
.STACK 64
.DATA
DATA1
DQ
548B9963CE7H
ORG
0010H
DATA2
DQ
3FCD4FA23B8DH
ORG
0020H
DATA3
DQ
?
MAIN
BACK:
each word is 2
bytes long.
MAIN
CMPE328 Spring 2007-08
.CODE
PROC
MOV
MOV
CLC
MOV
MOV
MOV
MOV
SI,OFFSET DATA1
DI,OFFSET DATA2
bx,OFFSET DATA3
CX,04
;SI is pointer for operand1
;DI is pointer for operand2
;BX is pointer for the sum
MOV
ADC
MOV
INC
INC
INC
INC
INC
INC
AX,[SI]
AX,[DI]
[BX],AX
SI
SI
DI
DI
BX
BX
;move the first operand to AX
;add the second operand to Ax
;store the sum
;point to next word of operad1
LOOP
BACK
; CONTUNUE ADDUNG for 4-words
MOV
INT
ENDP
END
AH,4CH
21H
;go back to DOS
FAR
AX,@DATA
DS,AX
6
Section 3.1
Multiple Word Addition – 2
write a
program
that adds
two
quadword
numbers
and saves
the result:
ds:0004
78
56
34
12
DF
9B
57
13
MOV AX,word ptr num1 ;first number LSW
ADD AX,word ptr num2 ; add second number LSW
MOV word ptr SUM,AX ; save LSW to SUM
MOV AX,word ptr num1+2 ;first number MSW
ADC AX,word ptr num2+2 ; add second number MSW with carry
MOV word ptr SUM+2,AX ; save MSW to SUM+2
Section 3.1
„Example
ds:0000
Multi Word Addition Exercise
„
Write a program to find the sum of signed
numbers -37, 126, 112, 15, 35, 41, 90.
„
Write a program to find the sum of
unsigned words 27354, 28521, 29553,
41280, 60606. Result may be multipleword.
Clear Carry for the LSW addition
;point to next word of operad2
;point to next word of sum
MAIN
Dr.Mehmet Bodur, EMU-CMPE
7
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
8
Section 3.1
Section 3.1
Example – 1
„
8086 SUB Instruction
Write a program to find the sum of signed
bytes -37, 126, 112, 15, 35, 41, 90.
.data
count equ 7
snum db -37,126,112 15,35,41,90
sum dw ?
.code
mov ax,@data
mov ds,ax
mov cx,count
mov bx,0
clc
mov si,offset snum
add_next:
mov al,[si]
cbw
adc bx,ax
inc si
dec cx
jnz add_next
mov sum,bx
CMPE328 Spring 2007-08
„
destination and source are similar with the add instruction.
Flags affected are: C S P A Z O;
Operands can be both signed or unsigned.
CF=1 means that a borrow taken from the next digit.
; alternate coding is
.data
count equ 7
snum db -37,126,112 15,35,41,90
sum dw ?
.code
mov ax,@data
mov ds,ax
mov cx,count
mov bx,0
clc
mov si,offset snum
add_next:
movsx bx,[si]
adc ax,bx
inc si
loop add_next
mov sum,bx
Dr.Mehmet Bodur, EMU-CMPE
sub dest, source
subtraction requires borrow propagation. Carry flag is
employed for Borrow.
„
Multi-word subtraction requires subtraction with borrow.
sbb dest, source
9
after execution dest = dest – source – CF
if CF=1 then dest = dest – source –1 ;
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
10
Section 3.1
Section 3.2
Multi-Word Subtraction
„
„
Example: Double-Word subtraction:
data_a
data_b
result
.
mov
sub
mov
mov
sbb
mov
. . .
dd 62562FAh
dd 412963Bh
dd ?
. .
ax, word ptr data_a
ax, word ptr data_b
word ptr result, ax
ax, word ptr data_a+2
ax, word ptr data_b+2
word ptr result+2, ax
62FA h – 963B h = CCBF h with CF=1
; ax Å LSW of data_a
; subtract LSW of data_b
; ax Æ LSW of result.
; ax Å MSW of data_a
; subtract with borrow
; ax Æ MSW of result.
625 h – 412 h – 1 = 212 h
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
Unsigned Multiplication
11
Multiplication generates longer result than operands:
mul op
Multiplies a byte by a byte, or a word by a word.
„
Multiplication
Oper.1 Oper.2.
Byte x byte
AL
reg. or mem AX
Result
Word x word
AX
reg. or mem DX,AX
In word x word case, double-word result goes to dx, ax.
dx returns MSW, and ax returns LSW of the result.
Example: multiply 50 by 20
Example: multiply 300 by 5
300>255 Î word x word required
both operands are byte.
mov al, 50
mov ax, 300
mov bx, 5
mov bl, 20
mul bl
; result is in ax
mul bx
; result is in dx.ax
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
12
Section 3.2
Section 3.2
Unsigned Division
„
Division generates a quotient and a reminder:
Unsigned Division Example
„
Example for dw/w.
„
; from the data segment
data1 dd 105432
data2 dw 10000
quotnt dw ?
remain dw ?
„
; from
mov
mov
div
mov
mov
Example: 325 /6 = 54 + 1/6 Æ Quotient=54, Reminder=1
div denum
Divides a word by a byte, or a double-word by a word.
div gives divide error interrupt when quotient exceeds AL
(for word/byte) or AX (for double-word/word case).
division
numer. denum.
word / byte
AX
Quotient Reminder
reg. or mem AL
AH
double word / word DX AX reg. or mem AX
DX
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
13
the code segment:
ax, word ptr data1
dx, word ptr data1+2
data2
quotnt, ax
remain, dx
Dr.Mehmet Bodur, EMU-CMPE
CMPE328 Spring 2007-08
14
Section 3.3
Section 3.3
Logic Instructions
„
„
AND, OR, XOR instructions clear CF and OF flags, and
change PF, ZF, SF according to the ALU result.
AND dst,src
„
„
Bitwise “or” operations.
“1” sets, “0” selects the related bit of the other.
Bitwise “exclusive-or” operations.
“1” toggles, “0” does not toggle the related bit of the other
operand.
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
15
op
0
0
op
CF
SHL op,1
and,
SHR op,1
instructions shifts op one bit right or left., and change C, P, Z, S, O
according to the ALU result.
SHL op,cl
and,
SHR op,cl
make repetitive shifts as many as the contents of cl.
XOR dst, src
CF
„
Bitwise “and” operations.
“1” selects, “0” clears the related bit of the other operand (it is
called masking the unwanted bits).
OR dst,src
„
Shift Instructions
Example: SHR AL,3 ; is not allowed.
Example MOV cl,3
SHR al, cl ; shifts al 3 bits right.
; Two least significant bits become lost,
; third bit becomes shifted into CF.
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
16
Section 3.3
Compare Instruction
Upper Case Conversion – 1
-0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -A -B -C -D -E -F
„
CMP
op1, op2
234567-
Compares
signed or unsigned numbers.
It changes flags C,S,Z,O,A,P according to
the result of op1 – op2.
But it does not change the register contents.
For unsigned numbers use JE, JA, JB, etc.
For signed numbers use JE, JL, JG, etc.
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
„
„
17
0
@
P
`
p
!
1
A
Q
a
q
"
2
B
R
b
r
#
3
C
S
c
s
$
4
D
T
d
t
%
5
E
U
e
u
&
6
F
V
f
v
'
7
G
W
g
w
(
8
H
X
h
x
)
9
I
Y
i
y
CMPE328 Spring 2007-08
MOV
INT
MAIN
END
AH,4CH
21H
ENDP
MAIN
CMPE328 Spring 2007-08
„
Dr.Mehmet Bodur, EMU-CMPE
AL, “a”
OVER
AL, “z”
OVER
AL, ‘a’ – ’A’
„
„
19
l
|
.
>
N
^
n
→
/
?
O
o
←
Dr.Mehmet Bodur, EMU-CMPE
ASCII strings are not little endian,
but unpacked-BCD is little-endian.
ASCII to unpacked- BCD
conversion:
Alternate Conversion
;go back to DOS
\
=
M
]
m
}
18
BCD and ASCII operations
„
MOV SI,OFFSET DATA1
;SI points to original data
MOV BX,OFFSET DATA2 ;BX points to uppercase data
MOV CX,14
;CX is loop counter
BACK:
MOV AL,[SI]
;get next char
CMP AL,61H
;if less than 'a'
JB
NONEED
;then no need to convert
CMP AL,7AH
;if greater than 'z'
JA
NONEED
;than no need to convert
AND AL,11011111B
;masj d5 to convert to uppercase
NONEED:
MOV [BX],AL
;store uppercase character
INC SI
;increment pointer to original
INC BX
;increment pointer to uppercase data
LOOP BACK
;continue looping if CX>0
,
<
L
Section 3.4
Upper Case Conversion – 2
CMP
JB
CMP
JA
SUB
+
;
K
[
k
{
Convert a text message to all upper case letters.
for each character ch, if ch>60h and ch<7Bh then
clear bit-5 of ch.
Both comparison
“c” = 0110 0011 Æ “C” = 0100 0011. are unsigned.
“u” = 0111 0101 Æ “U” = 0101 0101.
Section 3.3
.MODEL SMALL
.STACK 64
.DATA
DATA1
DB 'mY NAME is jOe'
ORG 0020H
DATA2
DB 14 DUP(?)
.CODE
MAIN
PROC
FAR
MOV AX,@DATA
MOV DS,AX
*
:
J
Z
j
z
Delete the upper nibble of the
ASCII coded digit.
Correct the byte-ordering.
-0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -A -B -C -D -E -F
2-
! " # $ % & ' ( ) * + , - . /
3- 0 1 2 3 4 5 6 7 8 9 : ; < = > ?
4- @ A B C D E F G H I J K L M N O
5- P Q R S T U V W X Y Z [
\
] ^ -
6- ` a b c d e f g h i j k l m n o
7- p q r s t u v w x y z { | } → ←
unpacked to packed- BCD conversion:
Write two unpacked BCD digit in one packed BCD digit.
Examples: Number 5 Æ ASCII 35h Æ unpacked-BCD 05
Number 7 Æ ASCII 37h Æ unpacked-BCD 07
Number 0 Æ ASCII 30h Æ unpacked-BCD 00
Number 1 Æ ASCII 31h Æ unpacked-BCD 01
packed in little
unpacked BCD 05 07 00 01 00 … Æ
endian convention
Packed-BCD 75 10 00 …
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
20
Section 3.4
Section 3.4
Packed-BCD to ASCII
BCD and ASCII add/sub
packed-BCD
Each Packed-BCD byte expands to two unpackedexpanded in little
BCD and ASCII code.
endian convention
Example:
p-BCD 29h Æ u-BCD 09h 02h
ASCII strings are in
reverse direction.
Æ ASCII 32h 39h
„
„
mov al, bcd
mov ah,al
and ax,0F00Fh
mov cl,4
shr ah,cl
or ax,3030h
xchg ah,al
mov asc, ax
CMPE328 Spring 2007-08
unpacked BCD
unpacked BCD
ASCII numbers
;p-bcd taken into al
;copy it into ah
;clear LS-nib of AH, MS in AL
;shift MS-nib 4-bit right
; and get both digits in LS-nib.
;combine with 30h to get ASCII
;swap for ASCII storage convent.
;store ASCII to memory location
Dr.Mehmet Bodur, EMU-CMPE
„
„
„
„
21
SUB dst, src
DAS
SUB AX, src
AAS
DIV src
AAD
SUB AX, src
AAS
OR AX,3030h
correction of multiplication and division work only with unpacked BCD.
packed BCD decimal adjust is available for both dst=AL, and dst=AX.
AAA clears the higher nibbles of AH and AL.
„
ADD dst, src
DAA
ADD AX, src
AAA
MUL src
AAM
ADD AX, src
AAA
OR AX,3030h
ASCII addition needs OR AX,3030h to convert the higher nibbles to 30h
DAA-AAA/DAS-AAS shall only be used after a BCD ADD/SUB operation.
AAM and AAD shall only be used after an unpacked BCD multiplication and
division.
Dr.Mehmet Bodur, EMU-CMPE
CMPE328 Spring 2007-08
22
Section 3.4
Section 3.4
ROL, ROR, RCL, RCR Instructions
„
ROL operand,1
„
ROR operand,1
„
RCL operand,1
„
RCR operand,1
„
„
CF
operand
operand
CF
xor ax,ax
mov cx, 16
mov bx, wdata
bitloop:
ror bx,1
adc al,0
aaa
loop bitloop
CF
Example: swap the nibbles of bl
mov cl,4
ror bl,cl
(bl=4Ch becomes bl=C4h).
Dr.Mehmet Bodur, EMU-CMPE
Write a code to count the number of “1”s in a list
of data-words, and display it on the screen.
.model small
.data
wdata dw 97F4h
cnt1
db ?,?, ‘$’
.code
mov ax,@data
mov ds,ax
CF
operand
operand
Rxx op,cl
rotates op by cl bits.
CMPE328 Spring 2007-08
Example: nr. of 1’s in a Word
23
CMPE328 Spring 2007-08
or ax, 3030h
; ascii conv
mov cnt1, ah ; MSB first,
mov cnt1+1, al ; LSB next.
mov dx, offset cnt1
mov ah, 09h
int 21h ; display a msg
; clear ax
; for 16 bits\
; ls-bit shifts in CF
; if CF=1, alÅal+1
; unpacked-BCD adjust
; for 16 bits.
mov ah, 4ch
int 21h ; exit to DOS
.stack 64
end
Dr.Mehmet Bodur, EMU-CMPE
24
Section 3.5
Section 3.5
Bitwise Operations in C
„
Embedded System programming industry
„
20%
Assembler Coding
60% C coding with inline assembly codes
20% other languages (C++, Basic, Forth etc.)
AND:
bitwise OR:
bitwise invert:
shift left 2 bits,
shift right 2 bits,
CMPE328 Spring 2007-08
data1 & 0x0F
data1 | 0xF0
~data1
data1<<2
data1>>2
Æ 0x0A
Æ 0xFA
Æ 0xD5
Æ 0xE8
Æ 0x0E
Dr.Mehmet Bodur, EMU-CMPE
25
What is the Next?
We have completed Mov, Jump, Call, and
basic ALU-instructions.
„ Next, we have to see some services of
BIOS and DOS programming.
„
Please solve the following problems (page 117 in
Mazidi-Mazidi) 1, 2, 7 (a, b, c, g, h, I, j, k, l, n,
o), 8 (a, b, c, e), 9 (a, b, c), 14, 16, 19, 20, 25
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
Program to display nr of “1”s in a word
#include <stdio.h>
void main(void) {
unsigned int w=0x97F4, ;
unsigned char ones, bits;
bits=16; ones = 0;
do{
if( w & 0x0001) ++ones;
w >>1; } while(--bits);
printf( “%i”, ones); }
Assume data1= 0x3A = 0b00111010 ,
bitwise
Programming in C
27
CMPE328 Spring 2007-08
Dr.Mehmet Bodur, EMU-CMPE
26