Why is LDAA 0,X Equivalent to LDAA 1,X+?

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This is equivalent to performing INCX after the LDAA 0,X instruction. In summary, LDAA 0,X and LDAA 1,X+ are equivalent because they both load the A accumulator with the address in the X register, but the latter also increments the X register. The offset of 1 in LDAA 1,X+ is necessary because the X register is post incremented, meaning it will be incremented after the instruction is executed. This ensures that the correct address is loaded into the A accumulator.
  • #1
seang
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I cannot understand why the following bits are equivalent:

Code: 
LDAA 0,X
INCX
;and
LDAA 1,X+


The 1 is throwing me off. Since the X register is post incremented, why is it necessary? I would think that LDAA 0,X+ would be equivalent to the first bit of code. What am I missing?
 
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  • #2
I don't program in HC 12 assembly, but is the first arguent to the LDAA instruction the register number?
 
  • #3
Right, I was thinking that might be a problem.

LDAA 0,X loads the A accumulator with the address stored in the X register, plus the offset (0, in this case).

LDAA 1,X+ loads the A accumulator with the address in the X register, plus the offset (1 in this case), and then increments the X register.
 

1. Why is LDAA 0,X equivalent to LDAA 1,X+?

LDAA stands for "Load Accumulator with Address" in assembly language. The number after the "LDAA" refers to the address of the data being loaded into the accumulator. In this case, 0,X and 1,X+ both refer to the address X, with the only difference being that 1,X+ will automatically increment the address by 1 after the data is loaded. Therefore, both instructions will load the same data into the accumulator, making them equivalent.

2. What is the purpose of using LDAA 0,X or 1,X+?

The purpose of these instructions is to load data from a specific memory address into the accumulator, which is a register used for arithmetic and logical operations. This allows the programmer to access and manipulate data stored in memory during the program's execution.

3. Can LDAA 0,X and LDAA 1,X+ be used interchangeably?

Yes, these instructions can be used interchangeably in most cases. However, if the data being loaded into the accumulator is being used for further operations, the use of LDAA 1,X+ may be preferred as it automatically increments the address for the next data load.

4. Are there any differences between LDAA 0,X and LDAA 1,X+?

The only difference between these two instructions is that LDAA 1,X+ will automatically increment the address by 1 after the data is loaded into the accumulator. This can be useful when accessing consecutive data stored in memory.

5. Can LDAA 0,X or LDAA 1,X+ be used to load data from any memory address?

Yes, these instructions can be used to load data from any memory address. However, it is important to ensure that the address being used is valid and contains the desired data. Improper use of these instructions can result in errors or unexpected behavior in the program.

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