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Embedded Systems

PIC16F84A Instruction Set

Eng. Anis Nazer

Second Semester 2016-

PIC mid range ALU

Instruction format

MNEMONIC operand(s)

● (^) Examples: ADDWF 0x21, 0 SUBLW 0x MOVWF 0x

Instruction Set ● Three categories:

1. Byte instructions : operate on bytes of data

Instruction Set ● Three categories:

3. Literal instructions: operand is in the instruction itself

Example ● (^) Describe briefly the operation of the following instructions:

CLRW

MOVLW 0x

MOVWF 0x0C

INCF 0x0C, 1

MOVF 0x0C, 0

ADDLW 0x

MOVWF 0x0D

Example ● Write instructions to perform the following calculation and store the result in location 0x 0x11 + 0x32 – 0x2E MOVLW 0x ADDLW 0x MOVWF 0x MOVLW 0x2E SUBWF 0x25, 1

Another Example ● (^) Write instructions to swap (exchange) the values stored in locations 0x20 and 0x

1. move the value in location 0x20 to a temporary location
2. move the value in location 0x21 to location 0x
3. move the value in the temporary location to location 0x MOVF 0x20, 0 MOVWF 0x MOVF 0x21, 0 MOVWF 0x MOVF 0x23, 0 MOVWF 0x

Assembler ● (^) For the MCU to understand the instruction, it has to be translated to machine language ● Example: translate the following instruction to machine language:

MOVLW 0xF

→ 11 0000 1111 0011 = 0x30F

BSF 0x2E, 4

→ 01 0010 0010 1110 = 0x122E

IORWF 0x3A , 1 →?

Assembler ● (^) Example: translate the following machine language instruction to

assembly: 0x19C

● 0x19C4 = 01 1001 1100 0100

BTFSC 0x44, 3

● 0x16B

BSF 0x35, 5

● 0x2A3C

Microchip Assembler format

LABEL MNEMONIC operand(s)

● (^) LABEL: any word (except mnemonics) ● (^) The label is optional, it is a reference point in the program ● (^) The MNEMONIC cannot start on the first character on a line ● (^) semi-colon used for comments ● (^) Ex. loop ADDWF 0x33, 1 Label MNEMONIC Operands

Example ● What does the following code do?

CLRF 0x

loop INCF 0x06 , 1

BTFSS 0x06 , 3

GOTO loop

CLRF 0x

Assembler directives ●

Assembler directives are commands to the

assembler

●

Directives are not part of the instruction set

●

So, they are not instructions for the PIC

●

They are not translated to machine language

●

They simplify writing the program

Assembler Directive: EQU ●

EQU: is an assembler directive used to define a

constant

●

for example:

age EQU 0x

●

here the assembler will find and replace all

occurrences of 'age' with 0x

age EQU 0x0F MOVLW D'23' MOVWF age MOVLW D'23' MOVWF 0x0F equivalent instructions