Hardware Stacks Question

[Luis Daniel Bolaños]

Hello everybody,

I'm learning about the PIC16F887 and trying to understand the concept of the 8 levels stacks of memory.

As far as I understand the stacks save the return point for a subroutine to keep working. So if I have 8 levels, I could only create 8 subroutines each one inside the other, is that right?

I don't get much about the concept. I need a simple explanation.

Thanks!!

 

[wp100]

Hi,

Yes you are correct.

Though not detailed in the 887 datasheet if you see the 877A datasheet section 2.3 it gives a clear description ( some later datasheets are cut down at bit)

This post also gives some useful info https://www.microchip.com/forums/m231223.aspx

 

[bigdogguru]

The following reference manual contains an in-depth discussion concerning the midrange PIC stack along with many other topics:

Reference: PICmicro MID-RANGE MCU FAMILY, Section:6.2.5 Stack, Page: 6-6

6.2.5 Stack

The stack allows a combination of up to 8 program calls and interrupts to occur. The stack contains
the return address from this branch in program execution.

Mid-Range MCU devices have an 8-level deep x 13-bit wide hardware stack. The stack space is
not part of either program or data space and the stack pointer is not readable or writable. The PC
is PUSHed onto the stack when a CALL instruction is executed or an interrupt causes a branch.
The stack is POPed in the event of a RETURN, RETLW or a RETFIE instruction execution. PCLATH
is not modified when the stack is PUSHed or POPed.

After the stack has been PUSHed eight times, the ninth push overwrites the value that was stored
from the first push. The tenth push overwrites the second push (and so on). An example of the
overwriting of the stack is shown in Figure 6-3.

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BigDog

 

[Luis Daniel Bolaños]

Thank you wp100 and bigdogguru! It helped me a lot. Now I get it