Question

Write an assembly code that converts an ASCII number (between 30H and 39H ) stored in a variable, named var, to a decimal number? Then, store this decimal value in register AL? However, if the ASCII value is not a number between (0-9) store FFH in register AL?

Answer 1

The assembly code checks if the ASCII value within variable 'var' is a digit (0-9). If so, it subtracts 30H to convert it to decimal, and stores the result in AL. Otherwise, AL is set to FFH.

Step-by-step explanation:

The task is to write assembly code that performs a specific conversion of an ASCII value to a decimal number. The variable 'var' contains the ASCII value. If the value of var is within the range of 30H to 39H, which represents the ASCII values for numbers 0 to 9, the equivalent decimal number is stored in the AL register. Otherwise, FFH is stored in AL to indicate an invalid input.

The following assembly code segment accomplishes this:

mov al, [var] ; Load the ASCII value from the variable into AL
cmp al, 30h ; Compare AL with the lower boundary of the ASCII numbers
jb invalid ; Jump if AL is below 30H (ASCII '0')
cmp al, 39h ; Compare AL with the upper boundary of the ASCII numbers
ja invalid ; Jump if AL is above 39H (ASCII '9')
sub al, 30h ; Subtract 30H to convert ASCII to decimal number
jmp done ; Skip the invalid label as conversion is done
invalid:
mov al, 0FFh ; Store FFH in AL to indicate an invalid input
done:

This code first loads the ASCII value from var into AL, then compares it to the ASCII ranges of characters '0' through '9'. If it falls within that range, it subtracts 30H from AL to convert the ASCII to its decimal equivalent. If the value is not within range, it sets AL to FFH.