Explanation
@R1
D-M
@temp
M=D // temp=R1
@RO
D=M
@R1
M=D
@R1
M=D // R1=RO
@temp
D=M
@RO
M=D
@temp
D=M
(END)
@END
0;JMP
1. @R1 : This line loads the memory location of R1 into the A-register, directing focus to R1's stored value.
2. D=M : This command copies the value from the A-register (originating from R1) into the D-register after loading R1's value into the A-register. Essentially, it creates a temporary variable, "temp," to store R1's value in the D-register.
3. @RO : This line functions similarly to step 1 but for the memory location RO, loading its value into the A-register.
4. D=M : This command transfers the data from the A-register (containing the value from RO) into the D-register, mirroring step 2.
5. @R1 : Again, we load the value from memory address R1 into the A-register.
6. M=D : Then, this command reinstates the value of RO, currently held in the D-register, to memory address R1. Since R1's value was preserved in "temp," the initial value of RO has effectively replaced R1's value, resulting in the swapping of R1 and RO's values.
7. @temp : This line loads the memory location "temp" into the A-register, essentially accessing the temporary storage where the initial value of R1 was kept.
8. D=M: This command replicates the contents of the A-register (holding the value from "temp") into the D-register, similar to the previous step.
9. @RO : Again, we load the value from memory address RO into the A-register.
10. M=D : This command retrieves the value from memory address RO and places it back into the D-register, which now holds the original value of R1. By returning the original value of R1 to RO, the exchange process is finalised.
11. (END) : This line appears to mark a location in the code with the label "END," serving to designate specific points for reference.
12. @END : In this scenario, the A-register is assigned the value "END." However, it's important to note that this isn't a valid jump instruction on its own, despite resembling an attempt to jump to the "END" label.
13. The jump instruction, 0;JMP, lacks qualification. It directs the computer to move to the address stored in the A-register. Here, the address is set to "END," which is a label rather than a specific address. This line seems to be a placeholder or an error, but it doesn't affect the logic of the swap operation.
The Flip.asm code operates as follows:
1. Initially, the programmer loads the value from register R1 into the D register.
2. The programmer then stores the value from the D register into a temporary register, which is crucial for preserving R1's value before it gets overwritten.
3. Next, the programmer loads the value from register RO into the D register.
4. The value from the D register is then stored into register R1, effectively swapping the values of R0 and R1.
5. Subsequently, the value stored in the temporary register is loaded into the D register and saved into register RO by the programmer, completing the switch operation.
6. Finally, the programmer executes a jump.