Microcontrollers

1
Microcontrollers

• 8051 Assembly Language

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What can the 8051 instructions do?

• Arithmetic (add, subtract, multiply, divide)
• Logical Operations (AND, OR, NOT, etc.)
• Data Transfer (move bytes)
• Boolean Variable Manipulation (move bits)
• Program Branching (branch, call subroutines)

3
Why does the uP need registers?

• Scratch pad.
• Math.
• Interface with the outside world.
• Timing and counting.
• Keep track of the program and interpret
  instructions.
• Point to data by holding addresses for easy
  reference.

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128 Bytes of On Chip RAM
Lower 64 Bytes
Upper 64 Bytes
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Scratch Pad on Chip RAM
80 byte addressable registers
128 addressable bits
32 register (Rn) addressable bytes
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The 4 Register Banks.
Numbered 0,1,2, and 3Only 1 at a time can be
activatedBank 0 is the default bank.
Rn
1 byte per register
Ri
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The Special Function Register Map
(upper 64 bytes of on chip RAM)
Mnemonic Address
Byte Address
Bit Address
8
MOV dest-byte, source-byteCopies bytes from the
source to the destination.

• MOV A, data
• MOV A, Rn
• MOV A, direct
• MOV A, _at_Ri
• MOV Rn, A
• MOV direct, A
• MOV _at_Ri, A
• MOV Rn, data

• MOV Rn, A
• MOV Rn, direct
• MOV direct, data
• MOV direct, _at_Ri
• MOV direct, Rn
• MOV _at_Ri, data
• MOV _at_Ri, A
• MOV _at_Ri, direct

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direct addressing

• direct any 8 bit address 00H to FFH.
• 2 byte instruction
• Can be used for any 8-bit address
• Example MOV A, 45H
• Copies the contents of RAM location 45H into the
  accumulator.
• Direct addresses may not start with a letter so
  use a leading zero as in 0E0H instead of E0H.

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Immediate (data) addressing

• data 8-bit number 00H to FFH.
• 10010110B (a binary number)
• 76H ( a hexadecimal number)
• 118 ( a decimal number)
• Example MOV A, 76H
• Makes the contents of the accumulator become 76H
• Data may not begin with a letter. Use a leading
  zero as in 0E0H instead of E0H.

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Register Addressing

• Rn any register in the selected register bank.
  (n 0,1,2,3,4,5,6,7)

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Indirect Addressing

• _at_Ri register 0 or register 1 in the selected
  register bank. ( i 0,1 only)
• Ri contains the address of the data.

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ADD A, source-byte

• Accumulator is always the destination byte.
• If there is a carry from E7, CY goes high.
• If there is an overflow, OV goes high.
• Direct addressing as in ADD A, 7FH
• Immediate addressing as in ADD A. 7FH

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The Stack

• The Stack is a continuous group of RAM memory
  locations.
• By default, the stack starts at 08H in RAM (Bank
  1) and may extend to RAM address 7FH.
• Uses the PUSH and POP instructions.
• PUSH places data on the stack
• POP takes data from the stack

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PUSH direct

• Example PUSH 0E0H
• Execution
• First, the stack pointer is incremented (1 is
  added).
• Second, the contents of RAM memory location E0H
  is copied to the address indicated by the stack
  pointer.

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POP direct

• Example POP 0E0H
• First the contents of the memory location
  indicated by the stack pointer is copied into RAM
  memory location E0H.
• Second, the stack pointer is decremented (1 is
  subtracted).

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The programming process
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.asm files

• Called the source code.
• Written in mnemonic form
• Created with software that is essentially a
  simple word processor.
• Keyboard entry.

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.obj files

• Called theobject file.
• The output of the assembler.
• In a format called the machine language

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.lst file

• Lists all the opcodes, operands, and addresses.
• Lists all of the programming syntax errors.

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Library files

• Can include any boilerplate code and often used
  subroutines.

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.abs files

• Called the absolute file.
• A marriage of all .obj files that have been
  linked together.

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.hex file

• Machine code that appears in hexadecimal form.
• Can be loaded into a ROM burner for programming
  the ROM chip.

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DB directive

• The DB directive tells the assembler that the
  8-bit number that follows is constant data and
  not an instruction.
• Example DB 28 causes 1CH to be stored in ROM .

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ORG directive

• Indicates the beginning address at which the
  program will be placed in ROM.

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EQU directive

• Assigns a literal name to to a number.
• Example THIS_YEAR EQU 2002
• Before assembly, the number 2002 will replace
  every instance of THIS_YEAR in the program.

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END directive

• Indicates the last line of the source code.