I want to use timer0 for a lot of timer

hello.At firstly I'm sorry for my terrible english.I design a circuit for car body control unit(BSI).I will control windsheld wipers(with rain sensor),car ceiling lamp,headlights,central locking etc. automatically with PIC16F877A.But ı have some problems about lightening system.I can use timer0 or timer2.For example,when you open the car's door,ceiling lamp will ON continuous.then you close the door,lamp will OFF 12 seconds later. I wrote asm code for 12 seconds.It works.NO problem.but I want that:After central locking is ON ,ceiling lamp will ON during 5 seconds.then It will OFF.And headlights will ON 20 seconds.How can I design algoritm and write asm code for this scenario.

I opened the door =>> ceiling lamp:ON
I closed the door =>> ceiling lamp:in normally will OFF 12 seconds later.But After 4 seconds from I closed door,I locked car.the ceiling lamp will OFF 5 seconds later.In totally,lamp will be OFF ,after 9 seconds.Also headlights will ON during 20 seconds.then it will OFF.

my asm code for 12 seconds: (ı must add 5 seconds and 20 seconds for central locking).

The method I use when several timers are needed is to use TMR0 or TMR1 to generate an interrupt at the period needed. If necessary, use a register to count interrupts if a longer period is needed. Then do this at each period. I leave it to you to convert it to assembler because it is so easy:

check if timer_a = 0. If it is, skip the next step
decrement timer_a
check if timer_b = 0. If it is, skip the next step
decrement timer_b
.
.
check if timer_z = 0. If it is return from the interrupt
decrement timer_z.
return from the interrupt.

If you do it this way you can have as many timers as you like and they all count down to zero and stop there. Supposing the period was 1 second, you could load timer_a with 6 and timer_b with 22 to get that many seconds delay. Then in your main loop all you do is check if they are zero to know if the period has elapsed. Timer_a will reach zero after 6 seconds and timer_b in 22 seconds. Remember that in PIC assembler, it is very easy to check if a register is zero or not, just use (example) "movf timer_a,f" and check if the Z flag has set or not.

Brian.