This PIC16F877A microcontroller tutorial answers the question, "How to implement a controllable digital clock using PIC16F877A ? "
Using PIC16 simulator (Proteus) you can verify this digital clock code and change it according to your needs. Using three push buttons (As shown in figure below) you can adjust time as you desire. This code is written in C language using MPLAB with HI-TECH C compiler. You can download this code from the 'Downloads' section at the bottom of this page.
The following diagram (made in Proteus) shows the PIC microcontroller circuit diagram.
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| Figure 1. PIC16F877A based controllable clock circuit |
The above figure was taken after setting time to 03:59:38, timer0 is used as the base for digital clock generation. Timer0 is used here to generate 1msec interrupts. After every 1msec a global variable named msCounter increments. When msCounter reaches a value of 1000 then another global variable named secCounter increments and this process repeats itself. Similarly, when secCounter reaches 60, then minCounter increments. And when minCounter reaches 60 then hrCounter increments. This process continues until hrCounter reaches 24 then all of these variables reset their values. LCD is updated with the new values of hrCounter, minCounter and secCounter after every second.
You can set time using three push buttons attached on RE0, RE1 and RE2 pins (As shown in the above figure). By pressing 'Set Time' button one time, code enters in configuration state. Hours value starts to blink and you can modify it using Up and Down buttons. Pressing Up button increments the value and pressing Down button decrements the value. When you are done setting Hours value, press 'Set Time' button again, then Minutes value will start to blink and you can adjust this value using Up and Down buttons. Similarly, after setting Minutes value, you can press 'Set Time' button again, then Seconds value will start to blink and you can adjust this value using Up and Down buttons. When you are done adjusting the time, then press 'Set Time' button for the last time and this clock will start to work normally.
A crystal of 4MHz value is used in this circuit, which makes this PIC16F877A run at a speed of 1MIPS (Million of instructions per second).