Here's some of that promised help.
The PIC16F628A has two vectors you need to set up. It's often done something like this:
ORG 000H
GOTO MAIN
ORG 004H
GOTO ALLINTS
ORG 010H
MAIN
When the processor comes out of reset, it will start at MAIN. But if an interrupt happens (from any source), it will then branch to ALLINTS. The names can be anything you want, though. But those will suffice here.
You can debounce any and all switches on PORTA, at once. (See the code I've provided for a different processor here: Differences between Interrupts and sampling for hardware button?
Your MAIN code will need to initialize the timer to my preference of \$8\:\textrm{ms}\$. I'll assume \$4\:\textrm{MHz}\$ is the operating clock rate. If you set up for a divide by 8, your counter will need to start out at -1000 and be reset to that, each interrupting event. Of course, you'll need to initialize variables and the TMR1 register and associated configuration bits in T1CON.
Some of the variables I'm considering might be placed in a CBLOCK, like this:
CBLOCK
SWDEBPREV
SWDEBCURR
T1_SAVEW
T1_SAVES
T1_STPREV
T1_STCURR
T1_SWPREV
T1_SWCURR
ENDC
You'll need a constant, like this:
COUNTDOWN EQU -1000
The MAIN code (replace the above example with the following) might start out something like this:
ORG 010H
MAIN
; TODO: Configure PORTA as required. Assume all switches are on PORTA.
CLRF INTCON
CLRF SWDEBPREV
CLRF SWDEBCURR
CLRF T1_SWPREV
CLRF T1_SWCURR
CLRF T1_STPREV
CLRF T1_STCURR
CLRF PIR1
BSF STATUS, RP0
CLRF PIE1
BSF PIE1, TMR1IE
BCF STATUS, RP0
MOVLW 34H
MOVWF T1CON
MOVLW LOW COUNTDOWN
MOVWF TMR1L
MOVLW LOW (COUNTDOWN >> 8)
MOVWF TMR1H
BSF INTCON, PEIE
BSF INTCON, GIE
BSF T1CON, TMR1ON
LOOP
; TODO: Use SWDEBCURR and SWDEBPREV here.
GOTO LOOP
That's before getting into the main LOOP which polls things.
Skip past the main loop for a minute and let's get to the interrupt routine. I've provided a link above which provides the basic logic of the state machine that can be applied to debounce a switch. But... it turns out that this state machine can be performed simultaneously on an entire port at one time, as easily as it is performed on one port pin. The processor works in 8-bit bytes, so why not take advantage of that?
The interrupt code might look like the following code. But be aware that I'm assuming (for now) that there is only one interrupt that has been enabled. I'm making this assumption because (1) I have no information about other interrupts; and, (2) it would greatly complicate things.
ALLINTS MOVWF T1_SAVEW
SWAPF STATUS, W
MOVWF T1_SAVES
BCF T1CON, TMR1ON
MOVLW LOW COUNTDOWN
MOVWF TMR1L
MOVLW LOW (COUNTDOWN >> 8)
MOVWF TMR1H
BSF T1CON, TMR1ON
MOVF SWDEBCURR, W ; Make the last debounced value
MOVWF SWDEBPREV ; the prior debounced value.
MOVF T1_STCURR, W ; Make the last switch state value
MOVWF T1_STPREV ; the prior switch state value.
MOVF T1_SWCURR, W ; Make the last raw port value
MOVWF T1_SWPREV ; the prior raw port value.
MOVF PORTA, W ; Read the port and save it as
MOVWF T1_SWCURR ; the current raw port value.
MOVWF SWDEBCURR ; Start as debounced value, too.
XORWF T1_SWPREV, W
MOVWF T1_STCURR
IORWF T1_STPREV, F
COMF W, W
ANDWF SWDEBCURR, F
MOVF T1_STPREV, W
ANDWF SWDEBPREV, W
IORWF SWDEBCURR, F ; Generate final debounced value.
MOVF T1_SAVES, W
SWAPF STATUS, W
MOVF T1_SAVEW, W
BCF PIR1, TMR1IF
RETFIE
I have tried to avoid any need to switch banks in the above code and that simplifies the state saving, just slightly. It's been a while (okay -- 10 years) since I've written PIC16 code. So please check it over carefully for mistakes. I think I got the basic inner logic correct. But the state saving and restoring is worth a close look. (Also note that in resetting TMR1 I felt I had to disable the counter long enough to load the next countdown value. This will cause the timing to "slide" a bit -- the time between interrupts won't be exactly \$8\:\textrm{ms}\$. But this is okay for just debouncing switches. So I didn't go to any further trouble about it.)
The MAIN code now only needs to observer the debounced states. If you want to look for a specific button value, you can read up SWDEBCURR and mask it with whatever appropriate mask is required to extract the specific pin and then just test the debounced bit value.
If, instead, you want to look for a debounced button change, then read up SWDEBCURR and XOR it with SWDEBPREV. Those bits that are then set to a 1 are cases where there has been a debounced button PRESS or RELEASE change.
Whichever choice you want is yours.
