ATmega324-Chap4-Assembly-Programming.pdf

Chapter 4
Assembly Language
How to write a program
The ATmega324 Microcontroller
Nguyễn Trung Hiếu 1
Nguyễn Trung Hiếu
Ref: Giáo trình Vi Xử Lý, BMĐT

Instruction Format
[LABEL] Mnemonic [Op1][Op2] [;comment]
• […]: optional
• Op: operand
• Example:
➢LOOP: INC R1 ; R1 R1 + 1
➢ LDI R16,20 ; R16 20
➢ BREQ LOOP ; LOOP is name of label, Operand1

Instruction Format
[LABEL] Mnemonic [Op1][Op2] [;comment]
• Operand can contain operators
• Example:
➢LDI R20,$0F&$75 ; R20  $05
➢LDI R22,255/7 ; R22  36
➢LDI R24,’A’<‘Z’ ; R24  1
➢LDI R26,HIGH($AB04) ; R26  $AB

Assembler Directives
• Instructions for the compiler, not assembly
• Control the assembler, don't create any code
• The leading dot must be in column 1 of the line
• Segment:
➢ Everywhere
➢ Header
➢ Code
➢ EEPROM
➢ SRAM

Assembler Directives: Everywhere
.ORG
Defines the address within the respective segment, where
the assembler assembles to
syntax: .ORG 0x0000
.INCLUDE
Includes a file and assembles its content, just like its content
would be part of the calling file
syntax: .INCLUDE <M324PDEF.inc>
.EXIT
End of the assembler-source code
(stops the assembling process)
.LIST
Switches the listing to the .LST-file on (the assembled code
will be listed in a readable text file .LST)
.NOLIST Switches the output to the .LST-file off, suppresses listing

Assembler Directives: Header
.DEF
Defines a synonym for a register
syntax: .DEF MyReg = R16
.SET
Defines a symbol and sets its value (later changes of this
value remain possible)
syntax: .SET test = 1234567
.EQU
Fixes the value of a symbol (later redefinition is not possible)
syntax: .EQU test = 1234567

Assembler Directives: Header
.ORG 0
.EQU COUNTER = $A0
.EQU MYADDR1=$08
.SET MYADDR2 = 0x18
LDI R26,MYADDR1 ;R26=$08
LDI R27,MYADDR2 ;R27=$18
LDI R16, COUNTER ;R16 = 0xA0
.SET MYADDR2=0X0B ;redefine MYADDR2=$0B
OUT MYADDR1,R16 ;MYADDR1≡PORTC=0xA0
OUT MYADDR2,R16 ;MYADDR2≡PORTD=0xA0

Assembler Directives: Code
.CSEG
Start of the code segment (all that follows is assembled to
the code segment and will go to the program space)
.DB
Inserts one or more constant bytes in the code segment
The number of inserted bytes must be even, otherwise an
additional zero byte will be inserted by the assembler
syntax: .DB 1,’a’,”bc”
.DW
Insert binary words in the code segment, not used string
syntax: .DW 5,’b’
.LISTMAC
Macros will be listed in the .LST-file.
(Default is that macros are not listed)
.MACRO
Beginning of a macro (no code will be produced, call of the
macro later produces code)
syntax: .MACRO macroname parameters
.ENDMACRO End of the macro

Assembler Directives: Code
;Define Macro LOADIO
.MACRO LOADIO
LDI R20,@1
OUT @0,R20
.ENDMACRO
;Call Macro LOADIO
LOADIO PORTA, $20 ;PORTA=$20
.EQU VAL_1 = $FF
LOADIO DDRC, VAL_1 ;DDRC=$FF
LOADIO SPL, $55 ;SPL=$55
@0 and @1 is input parameters
@ can up to 9

Assembler Directives: EEPROM
.ESEG
Assemble to the EEPROM-segment (the code produced will go
to the EEPROM section, the code produces an .EEP-file)
.DB
Inserts one or more constant bytes in the EEPROM segment
(could be numbers from 0..255, an ASCII-character like 'c', a
string like “abcde” or a combination like 1,2,3,'abc’)
syntax: .DB 1,’a’,”abcde”
.DW
Inserts a binary word to the EEPROM segment (the lower byte
goes to the next address, the higher byte follows on the
incremented address)
syntax: .DW 15,’d’

Assembler Directives: SRAM
.DSEG
Assemble to the data segment (here only BYTE directives and
labels are valid, during assembly only the labels are used)
.BYTE
Reserves one or more bytes space in the data segment (only
used to produce correct labels, does not insert any values!)

Assembler Directives: SRAM
.DSEG ; declare DATA segment
.ORG 0x120 ; SRAM, begin address at $120
VAR1: .BYTE 1 ; use 1 byte in SRAM for VAR1 at $120
.CSEG ; declare CODE segment
.ORG 0x10 ; FLASH, begin address = PC = $10
MOV R0,R1 ;
….. ;
….. ;
.ESEG ; declare EEPROM segment
VAR2: .BYTE 5 ; use 5 byte in EEPROM for VAR2

Instruction Types
• Data transfer
• Arithmetic
• Logical
• Boolean variable
• Program branching
• MCU control
Used for creating loops,
branching and call subroutine

Program Branching Types
• Call, Return
- Call subroutine: save information about where it currently is
executing and then jumps to the subroutine
- Return: when the subroutine is finished, it returns to where the
call was made
• Conditional Jump (Branch)
- If the Branch test is successful, the program jumps to the location
specified (no save information)
- If the Branch test is unsuccessful, the next line of code is executed
• Unconditional Jump (Jump)
- Always jump to the location specified (no save information)

Program Branching Types
Call, return
Conditional and
Unconditional Jump
Subroutine Loops, branching

Call and Return
MAIN: ... (1)
(RCALL,ICALL)CALL SUBLABEL (2)
... (3)
...
SUBLABEL: ... (4)
...
RET (5)
Structure:

Subroutine
▪ Divide and Conquer – Allow you to focus on one small “chunk”
of the problem at a time
▪ Code Organization – Gives the code organization and structure.
A small step into the world of object-oriented programming
▪ Hierarchical Design – Moves information about the program at
the appropriate level of detail
▪ Code Readability – Allows others to read and understand the
program in digestible “bites” instead of all at once
▪ Encapsulation – Insulates the rest of the program from changes
made within a procedure
▪ Team Development – Helps multiple programmers to work on
the program in parallel; a first step to configuration control

Cho một số BCD nén nằm ở địa chỉ $220 của bộ nhớ SRAM. Viết
chương trình đọc số BCD đó và xuất giá trị ra 2 LED 7 đoạn kết nối
với PORTA (nibble cao) và PORTC (nibble thấp) của vi xử lý.
Your Turn!

LDI R16,ENTRY_NUMBER
(LDI R17,$0)
LDI ZH,HIGH(TABLE<<1)
LDI ZL,LOW(TABLE<<1)
ADD ZL,R16
(ADC ZH,R17)
LPM R17,Z
TABLE: .DB data1, data2, data3, …
(Remember) Look-up Table DATA: 8 bits (byte)
Program Memory
Address High Byte Low Byte
data2 data1
data4 data3
… …
… …
TABLE’S ADDRESS
If ENTRY_NUMBER = 0,
Z POINT TO

Create the Table
D7 D6
g
D5
f
D4
e
D3
d
D2
c
D1
b
D0
a
0 0 1 0 0 0 0 0 0 40H
1 0 1 1 1 1 0 0 1 79H
2 0 0 1 0 0 1 0 0 24H
3 0 0 1 1 0 0 0 0 30H
4 0 0 0 1 1 0 0 1 19H
5 0 0 0 1 0 0 1 0 12H
6 0 0 0 0 0 0 1 0 02H
7 0 1 1 1 1 0 0 0 78H
8 0 0 0 0 0 0 0 0 00H
9 0 0 0 1 0 0 0 0 10H
TABLE: .DB $40,$79,$24,$30,$19,$12,$02,$78,$00,$10

.ORG 0
LDI R16,$FF
OUT DDRA,R16
OUT DDRC,R16
LDS R16,$220
ANDI R16,$0F
CALL LOOKUP
OUT PORTC,R17
LDS R16,$220
ANDI R16,$F0
SWAP R16
CALL LOOKUP
OUT PORTA,R17
LOOP: JMP LOOP
21
Solutions
PORTA,
PORTC
output
LOOKUP:
ADD ZL,R16
LPM R17,Z
RET
TABLE: .DB $40,$79,$24,$30,$19,$12,$02,$78,$00,$10
Gọi CTC lần 1
Gọi CTC lần 2

22
Analyze
LOOKUP:
ADD ZL,R16
LPM R17,Z
RET
▪ Subroutine named LOOKUP
▪ The input parameter is stored in R16
▪ The return parameter is stored in R17
▪ The subroutine can change value in R16 – to keep it safe
LOOKUP:
PUSH R16
….
POP R16
RET Nguyễn Trung Hiếu

Unconditional Jump
JMP: (Direct Program Addressing)
IJMP: (Indirect Program Addressing)
RJMP: (Relative Program Addressing)

Conditional Jumps
Instruction Abbreviation of Comment
BREQ label Branch if Equal Jump to location label, if Z = 1
BRNE label Branch if Not Equal Jump to location label, if Z = 0
BRCS label
BRLO label
Branch if Carry Set
Branch if Lower
Jump to location label, if C = 1
BRCC label
BRSH label
Branch if Carry Cleared
Branch if Same or Higher
Jump to location label, if C = 0
BRMI label Branch if Minus Jump to location label, if N = 1
BRPL label Branch if Plus Jump to location label, if N = 0
BRGE label Branch if Greater or Equal Jump to location label, if S = 0
BRLT label Branch if Less Than Jump to location label, if S = 1
BRHS label Branch if Half Carry Set Jump to location label, if H = 1
BRHC label Branch if Half Carry Cleared Jump to location label, if H = 0
BRTS label Branch if T flag Set Jump to location label, if T = 1
BRTC label Branch if T flag Cleared Jump to location label, if T = 0
BRIS label Branch if I flag set Jump to location label, if I = 1
BRIC label Branch if I flag cleared Jump to location label, if I = 0
H S V N C
Z
T
I
SREG

Conditional Jumps
Instruction Abbreviation of Comment
SBRS Rd,b Skip if Bit in Register is Set Skip next instruction if Rd(b) = 1
SBRC Rd,b Skip if Bit in Register is Cleared Skip next instruction if Rd(b) = 0
SBIS IO_Addr,b Skip if Bit in I/O Register is Set Skip next instruction if IO_Addr(b) = 1
SBIC IO_Addr,b Skip if Bit in I/O Register is Cleared Skip next instruction if IO_Addr(b) = 0
Branch with conditions of bits

Creating a Loop (1)
Viết chương trình thực hiện ghi giá trị $20 vào bộ nhớ SRAM từ ô
nhớ $200 đến $210
.ORG $0
LDI R16,$20
STS $200,R16
STS $201,R16
STS $202,R16
STS $203,R16
…
17 lần

Viết chương trình thực hiện ghi giá trị $20
vào bộ nhớ SRAM từ ô nhớ $200 đến
$210
.ORG $0
LDI R16,$20
LDI R17,17
LDI ZH,HIGH($200)
LDI ZL,LOW($200)
Again: ST Z+,R16
DEC R17
BRNE Again
Creating a Loop (2)
Ptr  $200
(Ptr)  R16
Ptr  Ptr+1
Loop=0?
N
Y
Loop  17
LoopLoop-1
R16  $20
Z = 0
Z = 1
SIMILAR TO FOR LOOPS

$210
.ORG $0
LDI R16,$20
LDI ZH,HIGH($200)
LDI ZL,LOW($200)
Again: ST Z+,R16
CPI ZL,$11
BRCS Again
Creating a Loop (3)
Ptr  $200
(Ptr)  R16
Ptr  Ptr+1
Ptr<=$210?
Y
N
R16  $20
C = 1
C = 0
ZL - $11
SIMILAR TO DO … WHILE …

$210
.ORG $0
LDI R16,$20
LDI ZH,HIGH($200)
LDI ZL,LOW($200)
Again: ST Z+,R16
CPI ZL,$11
BRNE Again
Creating a Loop (4)
Ptr  $200
(Ptr)  R16
Ptr  Ptr+1
Ptr=$211?
N
Y
R16  $20
Z = 0
Z = 1
ZL - $11
SIMILAR TO DO … WHILE …

Your Turn!
Cho một chuỗi số (có giá trị từ 0 đến 9) được lưu trong ô nhớ
$200 đến $210 ở bộ nhớ SRAM (mỗi ô lưu 1 số).
Viết chương trình tiến hành đọc giá trị từ các ô nhớ ra, sau đó
cộng giá trị đọc được thêm $30 và lưu vào vị trí cũ

Solutions (1)
(Ptr)  R16
.ORG $0
LDI R17,$30
LDI ZH,HIGH($200)
LDI ZL,LOW($200)
LDI R18,17
Again: LD R16,Z
ADD R16,R17
ST Z+,R16
DEC R18
BRNE Again
Ptr  $200
R16  (Ptr)
Ptr  Ptr+1
Loop=0?
N
Y
R16  R16+R17
R17  $30
Z = 0
Z = 1
Loop  17
Loop  Loop - 1

Solutions (2)
(Ptr)  R16
.ORG $0
LDI R17,$30
LDI ZH,HIGH($200)
LDI ZL,LOW($200)
Again: LD R16,Z
ADD R16,R17
ST Z+,R16
CPI ZL,$11
BRNE Again
Ptr  $200
R16  (Ptr)
Ptr  Ptr+1
Ptr=$211?
N
Y
R16  R16+R17
R17  $30
Z = 0
Z = 1

For loop – Application
To create a for loop control:
can use BRNE, BRCS (with CPI), …
Example: a 10-time loop
LDI R16,10
LOOP: (begin loop)
…
…
(end loop)
DEC R16
BRNE LOOP
(continue)

Use BRNE to create a 1000-time loop?
Ex: 1000 = 250.4 = 200.5 = 100.10 = 10.10.10
LDI R17,4
LOOP1: LDI R16,250
LOOP: (begin loop)
…
…
(end loop)
DEC R16
BRNE LOOP
DEC R17
BRNE LOOP1
(continue)

Viết chương trình thực hiện xóa thanh ghi R1, sau đó thực
hiện cộng cho R1 số 10 năm lần liên tiếp
Solution:
CLR R1
LDI R16,10
LDI R17,5
AGAIN: ADD R1,R16
DEC R17
BRNE AGAIN

CLR R1 ; 1 MC
LDI R16,10 ; 1 MC
LDI R17,5 ; 1 MC
AGAIN: ADD R1,R16 ; 1 MC
DEC R17 ; 1 MC
BRNE AGAIN ; True – 2 MCs
; False – 1 MC
Timing Program

CLR R1 ; 1 MC
LDI R16,10 ; 1 MC
LDI R17,5 ; 1 MC
AGAIN: ADD R1,R16 ; 1 MC
DEC R17 ; 1 MC
BRNE AGAIN ; True – 2 MCs
; False – 1 MC
Timing Program
1 time
5 times
4 times T
1 time F
Total time = (1 + 1 + 1).1 + (1 + 1).5 + 2.4 + 1 = 22 MCs
Or = (1 + 1 + 1).1 + (1 + 1 + 2).5 - 1 = 22 MCs
If fMC = 1 MHz → TMC = 1 µs → Total time = 22 µs

Blinky Program
PC0  1
Delay
PC0  0
Delay

.ORG 0
SBI DDRC,0
LOOP: SBI PORTC,0
CALL DELAY
CBI PORTC,0
CALL DELAY
RJMP LOOP
DELAY:
LDI R21,100
L1: LDI R20,250
L2: NOP
DEC R20
BRNE L2
DEC R21
BRNE L1
RET
Blinky Program
PC0  1
Delay
PC0  0
Delay
→ Waveform? Period? Frequency?

Blinky Program
250x(1+1+2) – 1 = 999 MCs
.ORG 0
SBI DDRC,0
LOOP: SBI PORTC,0
CALL DELAY
CBI PORTC,0
CALL DELAY
RJMP LOOP
DELAY:
LDI R21,100
L1: LDI R20,250
L2: NOP ; 1 MC
DEC R20 ; 1 MC
BRNE L2 ; 2/1 MC
DEC R21
BRNE L1
RET

Blinky Program
100x(999+1+1+2) – 1
= 100299 MCs
.ORG 0
SBI DDRC,0
LOOP: SBI PORTC,0
CALL DELAY
CBI PORTC,0
CALL DELAY
RJMP LOOP
DELAY:
LDI R21,100
L1: LDI R20,250 ; 1 MC
L2: NOP ; 1 MC
DEC R20 ; 1 MC
BRNE L2 ; 2/1 MC
DEC R21 ; 1 MC
BRNE L1 ; 2/1 MC
RET

Blinky Program
100299 + 1 + 4
= 100304 MCs
.ORG 0
SBI DDRC,0
LOOP: SBI PORTC,0
CALL DELAY
CBI PORTC,0
CALL DELAY
RJMP LOOP
DELAY:
LDI R21,100 ; 1 MC
L1: LDI R20,250 ; 1 MC
L2: NOP ; 1 MC
DEC R20 ; 1 MC
BRNE L2 ; 2/1 MC
DEC R21 ; 1 MC
BRNE L1 ; 2/1 MC
RET ; 4 MC

Blinky Program
100299 + 1 + 4
= 100304 MCs
.ORG 0
SBI DDRC,0
LOOP: SBI PORTC,0 ; 1 MC
CALL DELAY ; 4 + 100304 MCs
CBI PORTC,0 ; 1 MC
RJMP LOOP ; 2 MC
DELAY:
LDI R21,100 ; 1 MC
L1: LDI R20,250 ; 1 MC
L2: NOP ; 1 MC
DEC R20 ; 1 MC
BRNE L2 ; 2/1 MC
DEC R21 ; 1 MC
BRNE L1 ; 2/1 MC
RET ; 4 MC

Blinky Program
.ORG 0
SBI DDRC,0
LOOP: SBI PORTC,0 ; 1 MC
CBI PORTC,0 ; 1 MC
RJMP LOOP ; 2 MC
TH = 4 + 100304 + 1 = 100309 MCs
TL = 4 + 100304 + 2 + 1 = 100311 MCs

If fMC = 1MHz, 1 MC = 1 μs
→ tH = 100,309 MC = 100,309 μs
→tL = 100,311 MC = 100,311 μs
→ T = tH + tL = 200,620 μs
→ f = 1/T = 4.98 Hz
Blinky Program
tH tL
T
PC0  1
Delay tH
PC0  0
Delay tL

→ tH = tL ≈ tDELAY ≈ 100 x 250 x 4 MC = 100,000 MC = 100,000 μs
→ T ≈ 200,000 μs
→ f ≈ 5 Hz
Blinky Program - Estimating
PC0  1
Delay tH
PC0  0
Delay tL
DELAY:
LDI R21,100
L1: LDI R20,250 ; 1 MC
L2: NOP ; 1 MC
DEC R20 ; 1 MC
BRNE L2 ; 2/1 MC
DEC R21 ; 1 MC
BRNE L1 ; 2/1 MC
RET
4 MCs

Viết chương trình tạo 1 xung vuông có tần số 10 kHz ở
chân PC0. Giả sử rằng tần số fMC = 4MHz
10-kHz square wave

10-kHz square wave
tH tL
T
PC0  1
Delay tH
PC0  0
Delay tL
tH = tL

10-kHz square wave
fMC = 4MHz → 1 MC = 0,25 µs
f = 10 kHz → TH = TL = 100 µs = 4.100.0,25 µs = 4.100 MCs
DELAY:
LDI R20,100
L1: NOP ; 1 MC
DEC R20 ; 1 MC
BRNE L1 ; 2/1 MC
RET

10-kHz square wave, duty cycle 30%
tH tL
T
PC0  1
Delay tH
PC0  0
Delay tL
Viết chương trình tạo 1 xung vuông có tần số 10 kHz với
chu kỳ nhiệm vụ 30% ở chân PC0.
Giả sử rằng tần số fMC = 4MHz
Chu kỳ nhiệm vụ = D = TH/T

PC0  1
Delay tH
PC0  0
Delay tL
Viết chương trình tạo 1 xung vuông có tần số 10 kHz với
fMC = 4MHz → 1 MC = 0,25 µs
f = 10 kHz → T = 200 µs
TH = 0,3T = 60 µs = 4.60.0,25 µs = 4.60 MCs
TL = 0,7T = 140 µs
= 4.140.0,25 µs = 4.140 MCs

400-kHz square wave
fMC = 4MHz → 1 MC = 0,25 µs
f = 400 kHz → TH = TL = 2.5 µs = 10 MCs

Viết chương trình tạo 1 xung vuông có tần số 400 kHz và

CPI R16,$05
BRNE Skip
(Statement 1)
Skip: (Continue)
If … else … – Equal/Not Equal (1)
R16 = $05?
N
Y
Statement 1
Z = 0
Z = 1
CP R16,R17
BRNE Skip
(Statement 1)
Skip: (Continue)
R16 = R17?
N
Y
Statement 1
Z = 0
Z = 1

CPI R16,$05
BRNE Not_Eq
(Statement 1)
RJMP Next
Not_Eq: (Statement 2)
Next: (Continue)
If … else … – Equal/Not Equal (2)
R16 = $05?
N
Y
Statement 1
Z = 0
Z = 1
Statement 2

CPI R16,$05
BRCC LessThan
(Statement 1)
LessThan: (Continue)
If … else … –
Greater Than or Equal/Less Than (1)
R16 ≥ $05?
N
Y
Statement 1
C = 1
C = 0

CPI R16,$05
BRCS GrEqThan
(Statement 1)
GrEqThan: (Continue)
If … else … –
R16 < $05?
N
Y
Statement 1
C = 0
C = 1

Viết chương trình kiểm tra nội dung trong thanh ghi R16.
Nếu giá trị 5 ≤ R16 ≤ 10, xuất giá trị bù 1 của R16 ra PORTA.
Ngược lại, xuất giá trị bù 2 của R16 ra PORTA.
58
Ví dụ
.ORG $0
LDI R16,$FF
OUT DDRA,R16
CPI R16,5
BRCC LessThan
CPI R16,11
BRCS GrEqThan
LessThan:
NEQ R16
RJMP NEXT
GrEgThan:
COMP R16
NEXT: OUT PORTA,R16
NOP

CPI R16,$05
BRCC LessThan
(Statement 1)
RJMP Next
LessThan: (Statement 2)
Next: (Continue)
If … else … –
R16 ≥ $05?
N
Y
Statement 1
C = 1
C = 0
Statement 2

CPI R16,$05
BRCS GrEqThan
(Statement 1)
RJMP Next
GrEqThan: (Statement 2)
Next: (Continue)
If … else … –
R16 < $05?
N
Y
Statement 1
C = 0
C = 1
Statement 2

SBRS R16,0
(Statement 1)
(Continue)
If … else … – Bit in Register is set/cleared (1)
R16(0)=1?
Y
N
Statement 1
SBRC R16,0
(Statement 1)
(Continue)
R16(0)=0?
Y
N
Statement 1
Note: Statement 1
- 1 instruction
- If > 1 instruction, call subroutine

SBRS R16,0
RJMP BitSet
(Statement 2)
RJMP Next
BitSet: (Statement 1)
Next: (Continue)
If … else … – Bit in Register is set/cleared (2)
R16(0)=1?
Y
N
Statement 1
Statement 2

Cho 20 bytes nằm trong bộ nhớ SRAM bắt đầu tại địa chỉ $250.
Viết chương trình xuất các byte chẵn ra PORTA
63
Bit Testing (1)

64
Your Turn!
Cho 20 bytes nằm trong bộ nhớ SRAM bắt đầu tại địa chỉ $300.
Viết chương trình xuất các byte chẵn ra PORTA và các byte lẽ ra
PORTB

Cho 100 bytes số có dấu nằm trong bộ nhớ SRAM bắt đầu tại địa chỉ
$400. Viết chương trình xuất các số âm ra PORTA và các số dương ra
PORTB
Bit Testing (2)
65

66
References
• Giáo trình Vi xử lý, BMĐT
• Các tài liệu trên Internet không trích dẫn hoặc không ghi tác
giả

ATmega324-Chap4-Assembly-Programming.pdf

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