The INC instruction adds 1 to the the "A" register, and stores the result to a register, counter, or location in memory. For the latter, the address pointer must be setup before the INC writes to memory.

404A - Store the result to the "A" register.
404B - Store the result to the "B" register.
404C - Store the result to the "C" general purpose register.
404F - Store the result to the "F" output high register.

4040 - Store the result to memory, at the current active address.
4041 - Store the result to address pointer 1.
4042 - Store the result to address pointer 2.