Microcontrollers and YOU!

Pointers are a very fundamental part of programming, often you need to reference a memory location without directly addressing or calling it, pointers help us do that. With c/c++ pointers can be a little daunting because how they work isn't directly apparent. Luckily for us, assembly works directly with the ram of the MCU and using pointers is extremely easy and almost effortless.

The use of pointers with a PIC mcu is called indirect addressing. We use the FSR(File Select register) and INDF. Essentially we load the value we want to point to into FSR and we address it using INDF. Fairly simple, lets look at an example:

VALUE equ 0x20

movlw   0x03
movwf   VALUE
movlw   0x20
movwf   FSR
movf    INDF,w
movwf   PORTC

The value on port c will be 0x03

First, we set up our variable VALUE to the general purpose address of 0x20.
Then, we set it equal to 0x03
We move the value of 0x20 to FSR (the location of VALUE)
Then we move INDF (The value of the address we loaded into FSR in this case 0x03) to w
Then w to PORTC

Very simple, with this in place you can save memory and make your programs extremely efficient and quick. Using the FSR and INDF will be essential to any remotely complicated code such as communications and robotics and other advance topics.