You must dereference it as an unsigned char* to get a byte, then check if it is in the valid ASCII range of 32-127.
void *ptr = 0x4000;
unsigned char c = *(unsigned char*)ptr;
if ((c>=32) && (c<=127))
{
// Valid ascii
}
else
{
// Not ascii
}
The program in assembly language for the LC-3 (Little Computer 3) architecture that checks if the initial value in memory location x4000 is a valid ASCII code:
The Program
.ORIG x3000
LD R0, CHECK_ASCII ; Load the address of the ASCII check subroutine
LD R1, ASCII_ADDR ; Load the address of the memory location x4000
LDR R2, R1, #0 ; Load the content of x4000 into R2
JSR R0, CHECK_ASCII ; Call the ASCII check subroutine
; Your code here (handle the result)
CHECK_ASCII
LD R3, ASCII_MIN ; Load the minimum ASCII value (usually 32 for space)
LD R4, ASCII_MAX ; Load the maximum ASCII value (usually 126 for '~')
ADD R5, R2, R3 ; Subtract the minimum value
NOT R5, R5
ADD R5, R5, #1 ; Invert and add 1
ADD R6, R4, R2 ; Subtract the maximum value
BRN IS_VALID_ASCII ; If R5 and R6 are both non-negative, it's a valid ASCII code
BRnzp NOT_VALID_ASCII
IS_VALID_ASCII
; Handle the case when the ASCII code is valid
; You can place your code here
NOT_VALID_ASCII
; Handle the case when the ASCII code is not valid
; You can place your code here
ASCII_ADDR .FILL x4000 ; Memory location x4000
ASCII_MIN .FILL x0020 ; Minimum ASCII code (space)
ASCII_MAX .FILL x007E ; Maximum ASCII code (~)
.END
This program loads the value at memory location x4000 into R2 and checks if it falls within the valid ASCII code range (32 to 126). Depending on the result, you can add your code to handle the valid or invalid ASCII code cases.
Read more about ASCII code here:
https://brainly.com/question/20361136
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