Microcontroller 8051

1
Microcontroller 8051 Assembly Language
2
Numerical Bases Used in Programming

• Hexadecimal
• Binary
• BCD

3
Hexadecimal Basis

• Hexadecimal Digits
• 1 2 3 4 5 6 7 8 9 A B C D E F
• A10
• B11
• C12
• D13
• E14
• F15

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Decimal, Binary, BCD, Hexadecimal Numbers

• (43)10
• (0100 0011)BCD
• ( 0010 1011 )2
• ( 2 B )16

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Registers
SP
6
Memory mapping in 8051

• ROM memory map in 8051 family

4k
8k
7

• RAM memory space allocation in the 8051

8
Addressing Modes

• Register
• Direct
• Register Indirect
• Immediate
• Relative
• Absolute
• Long
• Indexed

9
Register Addressing Mode

• MOV Rn, A n0,..,7
• ADD A, Rn
• MOV DPL, R6
• MOV DPTR, A
• MOV Rm, Rn

10
Direct Addressing Mode

• Although the entire of 128 bytes of RAM can be
  accessed using direct addressing mode, it is most
  often used to access RAM loc. 30 7FH.
• MOV R0, 40H
• MOV 56H, A
• MOV A, 4 MOV A, R4
• MOV 6, 2 copy R2 to R6
• MOV R6,R2 is invalid !

11
Register Indirect Addressing Mode

• In this mode, register is used as a pointer to
  the data.
• MOV A,_at_Ri move content of RAM loc. where
  address is held by Ri into A ( i0 or 1 )
• MOV _at_R1,B
• In other word, the content of register R0 or R1
  is sources or target in MOV, ADD and SUBB
  insructions.

12
Immediate Addressing Mode

• MOV A,65H
• MOV R6,65H
• MOV DPTR,2343H
• MOV P1,65H

13
Relative, Absolute, Long Addressing

• Used only with jump and call instructions
• SJMP
• ACALL,AJMP
• LCALL,LJMP

14
Indexed Addressing Mode

• This mode is widely used in accessing data
  elements of look-up table entries located in the
  program (code) space ROM at the 8051
• MOVC A,_at_ADPTR
• (A,_at_APC)
• A content of address A DPTR from ROM
• Note
• Because the data elements are stored in the
  program (code ) space ROM of the 8051, it uses
  the instruction MOVC instead of MOV. The C
  means code.

15
Some Simple Instructions

• MOV dest,source dest source
• MOV A,72H A72H
• MOV R4,62H R462H
• MOV B,0F9H Bthe content of F9th byte of RAM
• MOV DPTR,7634H
• MOV DPL,34H
• MOV DPH,76H
• MOV P1,A mov A to port 1
• Note 1
• MOV A,72H ? MOV A,72H
• After instruction MOV A,72H the content of
  72th byte of RAM will replace in Accumulator.
• Note 2
• MOV A,R3 MOV A,3

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• ADD A, Source AASOURCE
• ADD A,6 AA6
• ADD A,R6 AAR6
• ADD A,6 AA6 or AAR6
• ADD A,0F3H AA0F3H
• SUBB A, Source AA-SOURCE-C
• SUBB A,6 AA-6
• SUBB A,R6 AAR6

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MUL DIV

• MUL AB BA AB
• MOV A,25H
• MOV B,65H
• MUL AB 25H65H0E99
• B0EH, A99H
• DIV AB A A/B, B A mod B
• MOV A,25
• MOV B,10
• DIV AB A2, B5

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• SETB bit bit1
• CLR bit bit0
• SETB C CY1
• SETB P0.0 bit 0 from port 0 1
• SETB P3.7 bit 7 from port 3 1
• SETB ACC.2 bit 2 from ACCUMULATOR 1
• SETB 05 set high D5 of RAM loc. 20h
• Note
• CLR instruction is as same as SETB
• i.e.
• CLR C CY0
• But following instruction is only for CLR
• CLR A A0

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• DEC byte bytebyte-1
• INC byte bytebyte1
• INC R7
• DEC A
• DEC 40H 4040-1

20

• RR RL RRC RLC A
• EXAMPLE
• RR A
• RR
• RRC
• RL
• RLC

21

• ANL - ORL XRL
• Bitwise Logical Operations
• AND, OR, XOR
• EXAMPLE
• MOV R5,89H
• ANL R5,08H
• CPL A 1s complement
• Example
• MOV A,55H A01010101 B
• L01 CPL A
• MOV P1,A
• ACALL DELAY
• SJMP L01

22
Stack in the 8051

• The register used to access the stack is called
  SP (stack pointer) register.
• The stack pointer in the 8051 is only 8 bits
  wide, which means that it can take value 00 to
  FFH. When 8051 powered up, the SP register
  contains value 07.

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Example MOV R6,25H MOV R1,12H MOV R4,0F3H
PUSH 6 PUSH 1 PUSH 4
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LOOP and JUMP Instructions
Conditional Jumps
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• DJNZ
• Write a program to clear ACC, then
• add 3 to the accumulator ten time
• Solution
• MOV A,0
• MOV R2,10
• AGAIN ADD A,03
• DJNZ R2,AGAIN repeat until R20
  (10 times)
• MOV R5,A

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• LJMP(long jump)
• LJMP is an unconditional jump. It is a 3-byte
  instruction. It allows a jump to any memory
  location from 0000 to FFFFH.
• AJMP(absolute jump)
• In this 2-byte instruction, It allows a jump to
  any memory location within the 2k block of
  program memory.
• SJMP(short jump)
• In this 2-byte instruction. The relative address
  range of 00-FFH is divided into forward and
  backward jumps, that is , within -128 to 127
  bytes of memory relative to the address of the
  current PC.

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CALL Instructions

• Another control transfer instruction is the CALL
  instruction, which is used to call a subroutine.
• LCALL(long call)
• This 3-byte instruction can be used to call
  subroutines located anywhere within the 64K byte
  address space of the 8051.

• ACALL (absolute call)
• ACALL is 2-byte instruction. the target address
  of the subroutine must be within 2K byte range.

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• Example
• Write a program to copy a block of 10 bytes from
  RAM location starting at 37h to RAM location
  starting at 59h.
• Solution
• MOV R0,37h source pointer
• MOV R1,59h dest pointer
• MOV R2,10 counter
• L1 MOV A,_at_R0
• MOV _at_R1,A
• INC R0
• INC R1
• DJNZ R2,L1

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Decimal Addition

• 156 248

16 Bit Addition
1A44 22DB
3D1F

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Performing the Addition with 8051
1.Add the low bytes R7 and R5, leave the answer
in R3. 2.Add the high bytes R6 and R4, adding
any carry from step 1, and leave the answer in
R2. 3.Put any carry from step 2 in the final
byte, R1.
31
Steps 1, 2, 3
MOV A,R7 Move the low-byte into the accumulator
ADD A,R5 Add the second low-byte to the
accumulator MOV R3,A Move the answer to the
low-byte of the result
MOV A,R6 Move the high-byte into the accumulator
ADDC A,R4 Add the second high-byte to the
accumulator, plus carry. MOV R2,A Move the
answer to the high-byte of the result
MOV A,00h By default, the highest byte will be
zero. ADDC A,00h Add zero, plus carry from
step 2. MOV R1,A Move the answer to the
highest byte of the result
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The Whole Program
Load the first value into R6 and R7 MOV R6,1Ah
MOV R7,44h Load the first value into R4 and
R5 MOV R4,22h MOV R5,0DBh Call the 16-bit
addition routine LCALL ADD16_16 ADD16_16
Step 1 of the process MOV A,R7 Move the
low-byte into the accumulator ADD A,R5 Add the
second low-byte to the accumulator MOV R3,A
Move the answer to the low-byte of the result
Step 2 of the process MOV A,R6 Move the
high-byte into the accumulator ADDC A,R4 Add
the second high-byte to the accumulator, plus
carry. MOV R2,A Move the answer to the
high-byte of the result Step 3 of the process
MOV A,00h By default, the highest byte will be
zero. ADDC A,00h Add zero, plus carry from
step 2. MOV MOV R1,A Move the answer to the
highest byte of the result Return - answer now
resides in R1, R2, and R3. RET
33
Timer Port Operations

• Example
• Write a program using Timer0 to create a 10khz
  square wave on P1.0
• MOV TMOD,02H 8-bit auto-reload mode
• MOV TH0,-50 -50 reload value in TH0
• SETB TR0 start timer0
• LOOP JNB TF0, LOOP wait for overflow
• CLR TF0 clear timer0 overflow flag
• CPL P1.0 toggle port bit
• SJMP LOOP repeat
• END

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Interrupts

• Enabling and Disabling Interrupts
• Interrupt Priority
• Writing the ISR (Interrupt Service Routine)

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Interrupt Enable (IE) Register

• EA Global enable/disable.
• --- Undefined.
• ET2 Enable Timer 2 interrupt.
• ES Enable Serial port interrupt.
• ET1 Enable Timer 1 interrupt.
• EX1 Enable External 1 interrupt.
• ET0 Enable Timer 0 interrupt.
• EX0 Enable External 0 interrupt.

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Interrupt Vectors
37
Writing the ISR

• Example
• Writing the ISR for Timer0 interrupt
• ORG 0000H reset
• LJMP MAIN
• ORG 000BH Timer0 entry point
• T0ISR . Timer0 ISR begins
• .
• RETI return to main program
• MAIN . main program
• .
• .
• END

38
Structure of Assembly language and Running an
8051 program
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Examples of Our Program Instructions

• MOV C,P1.4
• JC LINE1
• SETB P1.0
• CLR P1.2

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8051 Instruction Set
ACALL Absolute Call ADD, ADDC Add Acc. (With
Carry) AJMP Absolute Jump ANL Bitwise
AND CJNE Compare Jump if Not Equal CLR
Clear Register CPL Complement Register DA
Decimal Adjust DEC Decrement Register DIV
Divide Accumulator by B DJNZ Dec. Reg. Jump
if Not Zero INC Increment Register JB Jump if
Bit Set JBC Jump if Bit Set and Clear Bit
JC Jump if Carry Set JMP Jump to Address JNB
Jump if Bit Not Set JNC Jump if Carry Not
Set JNZ Jump if Acc. Not Zero JZ Jump if
Accumulator Zero LCALL Long Call LJMP Long
Jump MOV Move Memory MOVC Move Code
Memory MOVX Move Extended Memory MUL Multiply
Accumulator by B NOP No Operation ORL Bitwise
OR POP Pop Value From Stack
PUSH Push Value Onto Stack RET Return From
Subroutine RETI Return From Interrupt RL
Rotate Accumulator Left RLC Rotate Acc. Left
Through Carry RR Rotate Accumulator Right RRC
Rotate Acc. Right Through Carry SETB Set
Bit SJMP Short Jump SUBB Sub. From Acc. With
Borrow SWAP Swap Accumulator Nibbles XCH
Exchange Bytes XCHD Exchange Digits XRL
Bitwise Exclusive OR Undefined Undefined
Instruction