Write an 8086 assembly program that:
- Load AL by an arbitrary number,
- Check whether it is an odd/even number,
- If it is an odd number, it will be converted to its next larger even number and will be shown in port 0 in the trainer kit.
- If it is an even number, it will be converted to its previous smaller odd number and will be shown in port 0 in the trainer kit.
Assuming we are using an ASCII code representation for the numbers to be shown in port 0, here's an example program:
```
; The arbitrary number is loaded in AL by the BIOS or other program.
start:
; Check whether AL is odd or even.
mov bl, 2 ; BL = 2 (the divisor for even/odd check)
xor ah, ah ; Clear AH to prepare for division
div bl ; Divide AL by BL, remainder is in AH
; Check the remainder: if it's zero, AL is even; otherwise, it's odd.
cmp ah, 0
je even
; AL is odd - convert to next larger even number.
add al, 1
odd:
; Convert the number to ASCII and show it in port 0.
add al, 30h ; Convert to ASCII digit
mov ah, 1
mov cx, 1
int 21h ; Use DOS interrupt for serial port output
jmp end
even:
; Convert the number to previous smaller odd number.
sub al, 1
; Skip output if AL is negative (no odd number below 1).
cmp al, 0
jl end
; Convert the number to ASCII and show it in port 0.
add al, 30h ; Convert to ASCII digit
mov ah, 1
mov cx, 1
int 21h ; Use DOS interrupt for serial port output
end:
; End of program.
ret
```
Sure! Here's a step-by-step guide to writing an 8086 assembly program that accomplishes the given tasks:
Step 1: Set up the necessary code and data segments
- Begin by setting up the code and data segments using the ".model small" directive.
- Define a stack segment for storing data temporarily, if required.
Step 2: Define constants and variables
- Define a constant to hold the value for the port number, let's assume it's called "portNum" and set its value to 0.
- Define a variable to store the input value, let's call it "inputVal".
Step 3: Write the main program
- Start the main program by using the "main" label.
- Prompt the user to input a number and store it in the "inputVal" variable using the appropriate input instruction, such as "mov ah, 01h" followed by "int 21h".
- Check if the number is odd or even by using the "test" instruction.
- If the number is odd, jump to the "oddNumber" label.
- If the number is even, jump to the "evenNumber" label.
Step 4: Handle odd numbers
- Jump to the "oddNumber" label.
- Add 1 to the "inputVal" variable to get the next larger even number using the "add" instruction.
- Output the new even number stored in "inputVal" to the specified port using the appropriate output instruction, such as "out dx, al" with the "portNum" value in the DX register.
Step 5: Handle even numbers
- Jump to the "evenNumber" label.
- Subtract 1 from the "inputVal" variable to get the previous smaller odd number using the "sub" instruction.
- Output the new odd number stored in "inputVal" to the specified port using the appropriate output instruction, such as "out dx, al" with the "portNum" value in the DX register.
Step 6: End the program
- After handling the odd and even numbers, end the program using the "int 20h" instruction.
Here's the assembly code that incorporates the above steps:
```
.model small
.stack
.data
portNum equ 0
inputVal db ?
.code
main:
; Prompt the user for input
mov ah, 01h
int 21h
; Store the input value in inputVal
sub al, 30h
mov inputVal, al
; Check if the number is odd or even
test al, 01h
jnz oddNumber ; Jump if odd
evenNumber:
; Handle even numbers
sub inputVal, 1
out dx, al ; Output to portNum
jmp endProgram
oddNumber:
; Handle odd numbers
add inputVal, 1
out dx, al ; Output to portNum
endProgram:
; End the program
int 20h
end main
```
Note: The code assumes that the trainer kit has the necessary instructions for input and output using ports. Make sure to adjust the code to match the specific configuration of your trainer kit.