Auto-decrement addressing can be used with arrays to efficiently traverse the array in reverse order. It simplifies the process of accessing elements from the end of the array to the beginning without the need for explicit pointer manipulation. Here’s how you can use auto-decrement addressing with arrays:
Assuming you have an array of integers stored in memory, and you want to process the elements in reverse order:
; Assume R1 contains the memory address of the last element of the array
; R2 can be used as a counter to keep track of the number of elements processed
MOV R1, #216 ; Load the memory address of the last element into register R1 (address 200 + 4 * (number of elements - 1))
MOV R2, #0 ; Initialize a counter in R2 to access elements sequentially
LOOP:
LOAD R3, [R1]- ; Load the value at the memory address pointed by R1 and decrement R1
; Here, you can perform operations with the value in R3 (e.g., print, compare, etc.)
; Example: Print the value in R3 (assuming an output routine to display R3 value)
OUT R3
INC R2 ; Increment the counter to move to the next element
CMP R2, #10 ; Compare the counter with the number of elements in the array (10 in this case)
JNZ LOOP ; Jump back to LOOP if the counter is not equal to 10 (i.e., not all elements processed)The [R1]- auto-decrement addressing mode is used to access each element of the array in reverse order. The loop starts with R1 pointing to the last element of the array (address 200 + 4 * (number of elements – 1)). After loading the value of the current element, R1 is automatically decremented by 4 (assuming each integer element occupies 4 bytes), so the next access will be to the previous element in the array.
