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These instructions have a format similar to the indexed addressing instructions discussed on the previous slide, but the constant has a different meaning. When the index register is auto-adjusted, the constant indicates the amount to add or subtract from the index register.
The first instruction above loads register A with the value pointed to by the contents of the X register and then increments the value in register X by two. The next instruction subtracts 4 from index register X and then loads into register A the value pointed to by the contents of the X register.