Countdown Timer using AT89S51

[Lanz]

Hi guys.
Im new to assembly programming.
I want to do a countdown timer using AT89S51.
So,i need u guys help.

Here how the hardware goes:
1)Double 7 segment to show the countdown time.
2)A buzzer that will beep once a second from the countdown starts till ends.
3)A switch to start the timer and a switch to Reset the timer.
4)2 switch to set the duration(A switch for x10 increment and a switch for x1 increment)
5)A switch to select between minutes and seconds.
6)2 outputs to relays.
7)An indicator to show minutes or seconds(LED or 7 segment)

And if possible,i want the timer or the 7 segment to go to the sleep mode after the countdown ends.All switches is push button type.

I dont know how to write the program in ASM.So anyone can help me with the programming?

[mik3]

First, you have to post your circuit if someone will help you.

[blueroomelectronics]

Post your schematic.

[Lanz]

The circuit will work i think.
I just simply draw it.

[hspalm]

You have to refer to the at89s manual for timer functions, as the timer functions (especially programmed with assembly) is to difficult to learn by scratch trough a forum thread. By the way, your ULN transistor array is placed reversed? The digital/low current signal goes from left to right. Also, why use a an array of 8 darlington transistors, when you can use much cheaper 2x regular darlington transistors?

And I don't think your buzzer will buzz by digital signal alone, you should amplify it through one of the 6 free lines on the ULN.