LSN 3 Assembly Language Programming

Department of

Engineering Technology

LSN 3

Assembly Language Programming

ECT358 – Microprocessors II

ECT 358 Microprocessors II [email protected]

LSN 3 – Program Structure

• Assembler directives

• Assembly language instructions

• Comments


LSN 3 – Program Structure

• Elements of an Assembly Language Statement

– Label

• Start with alphabetic character or underscore

– May contain any alphanumeric character, underscores, and question

marks

– Mnemonics

• Can be an assembly instruction mnemonic or assembly directive

– Operands

– Comment


LSN 3 – Assembler Directives

• MPASM directives

– Control directives – permit sections of conditionally

assembled code

– Data directives – control allocation of memory and refer to

data items symbolically

– Listing directives – control MPASM listing file format

– Macro directives – control execution and data allocation

within macro body definitions

– Object file directives – used when creating an object file



• Control directives

if version == 100

movlw D’10’

movwf io1,A

else

movlw D’26’

movwf io2,A

endif

end ; end of program

radix dec ; set default radix to decimal



• Control directives (cont.)

reset code 0x00

goto start

#define loop_cnt 30

#define sum3(x,y,z) (x + y + z)

#define seed 103

#include <p18F4520.inc> ;include the file

p18F8680.inc from

the installation

directory of mplab



• Data directives led_pat db 0x30,0x80,0x6D,9x40,0x79,0x20

msg1 db “Please enter your choice (1/2):”,0

array dw 0x1234,0x2300,0x40,0x33

msg2 dw “The humidity is “,0

TH equ 200

variable



• Macro directives

sum_of_3 macro arg1, arg2, arg3 ; WREG[arg1]+[arg2]+

; [arg3]

movf arg1,W,A

addwf arg2,W,A

addwf arg3,W,A

endm

sum_of_3 0x01,0x02,0x03 ; WREG[0x01]+[0x02]+

; [0x03]



test_mac macro chk_cnt

variable i

i = 0

while i < chk_cnt

movlw i

i += 1

endw

endm

start

test_mac 6

end


LSN 3 – Programming Logic


LSN 3 – Arithmetic Operations

• PIC18 MCU provides instructions for 8-bit addition,

subtraction, and multiplication

• Addition instructions addwf 0x30,W,A

addwfc 0x30,F,A

addlw 5

• Multi-byte addition

– Operated from LSB to MSB

– Must use carry bit in addition operations



• Subtraction instructions subfwb 0x30,W,A

subwf 0x30,W,A

subwfb 0x30,F,A

sublw 5

• Multi-byte subtraction

– Operated from LSB to MSB

– Must use borrow bit in subtraction operations



• Multiplication instructions mullw 5

mulwf 0x30,A


LSN 3 – Iterative Operations


LSN 3 – Table Operations

• Ability to store data in the 16-bit program memory

space

• Two instructions are provided that allow processor to

move bytes between program memory and data

memory

– Table read (TBLRD)

– Table write (TBLWT)


LSN 3 – Table Operations

• The table pointer addresses a byte within the program

memory and consists of three registers


LSN 3 – Logic Operations

• Applications of Logic Instructions

– Set a few bits in a byte

– Clear certain bits in a byte

– Toggle certain bits in a byte


LSN 3 – Programming Timing

• Instruction execution time is measured by using the

instruction cycle clock

– 1 instruction cycle = 4 crystal oscillator clock period

• Time delays are often needed to synchronize

operations or provide a set period of execution

– Hardware (timers)

– Software (instructions)


LSN 3 – Rotate Operations

• Used to manipulate bit fields and multiply/divide a

number


LSN 3 – Rotate Operations

• Divide and multiply by 2 can be performed by shifting

to the right and left

• Shift instruction make use of the rotate through carry

instructions with a cleared carry flag


LSN 3 – Homework

• Reading

– 2.1 – 2.15

– Is Assembly Language Obsolete.pdf

• Assignment – HW2

– E2.3, E2.7, E2.14, E2.19, E2.23

• References

– Microchip MCU2121 Course Notes

– Huang, H., PIC Microcontroller: An Introduction to

Software & Hardware Interfacing, Delmar Cengage

Learning 2007

Is Assembly Language Obsolete.pdf

LSN 3 Assembly Language Programming

Documents

Transcript of LSN 3 Assembly Language Programming