Question

2. Given variables A, B and C; each holding an 8-bit unsigned number. Write an AVR assembly program to find the average of A to C, placing the result into variable F.

-embedded system-

Answer 1

Write an AVR assembly language code to find the average of A to C variables, placing the result into variable F:

Provided variables A, B and C are holding an 8-bit unsigned number.

Assembly code:

.DSEG

A: .BYTE 1

B: .BYTE 1

C: .BYTE 1

F: .BYTE 1

.CSEG

Average:

lds r18, A

lds r19, B

lds r20, C

add r18, r19

lsr r18

add r19, r20

lsr r19

add r18, r19

lsr r18

sts F, r18

rjmp Average

Description:

.DSEG ; Data segment or Data space

A: .BYTE 1 ; Variable A

B: .BYTE 1 ; Variable B

C: .BYTE 1 ; Variable C

F: .BYTE 1 ; Result Variable F

.CSEG ; Code segment or Code space

Average: ; Procedure Average

lds r18, A ; Loads a single byte from the labeled data space A to r18 register.

lds r19, B ; Loads a single byte from the labeled data space B to r19 register.

lds r20, C ; Loads a single byte from the labeled data space C to r20 register.

add r18, r19 ; Addition of two register. r18 = r18 + r19

lsr r18 ; Logically shift right that divides by two.

add r19, r20 ; Addition of two register. r19 = r19 + r20

lsr r19 ; Logically shift right that divides by two.

add r18, r19  ; Addition of two register. r18 = r18 + r19

lsr r18   ; Logically shift right that divides by two.

sts F, r18 ; Stores a single byte from the r18 Register to the labeled data space F.

rjmp Average ; Relative jump to Average