a Consider the following program execute one instruction at

a. Consider the following program, execute one instruction at a time and list content of the R20 register. ldi r20, 0xBA Isr r20 lsr r20 lsr r20 lsr r20 lsr r20

Solution

(a)

ldi r 20, 0xBA ; Load Immediate BA (binary = 10111010) in r20

lsr r20 ; Logical Shift Right- Shifts all bits in Rd one place to the right. Bit 7 is cleared. Bit 0 is loaded into the C flag. This operation effectively divides an unsigned value by two. Thus r20 value

after instruction operation

lsr r20 ;

after instruction operation

lsr r20 ;

after instruction operation

lsr r20 ;

after instruction operation

lsr r20 ;

after instruction operation

(b) Program

convert decimal number in hex; Decimal 255 = hex FF

ldi r 20, 0xFF ; Load immediate FF (Decimal 255)

Loop:

SUBI r20, 04H ; Subtract imediate by 04 ie r20 = r20 - 04

rjump Loop ; jump to Loop

This will give result 255, 251, 247, 243...... (all numbers in decimal)

1

0

1

1

1

0

1

0

C =0