AT89S51 microcontroller-based timing alarm circuit diagram

Design a simple timer alarm microprocessor controlled. Requirements according to the initial value set (1-59 seconds) countdown timer to 0:00 when digital tube flashes "00" (at 1Hz flashing), the key features are as follows:

　　(A) setting key: When the countdown mode, press this button to stop the countdown after enter setting mode; If you have already set up a state in this key is invalid. (2) by a key: When setting the state, each time the increment key figures of the initial value by one. (3) delivery of a key: When setting state, decreasing each time the key figures of the initial value minus 1. (4) Enter key: After setting state, press this button, SCM initial value under the new countdown and display digital countdown. If the state is already in the timing of this key is invalid.

Figure timing alarm circuit schematics