📖 10. Programmable Keyboard and Display Interface: 8279
📖 From An Introduction To Microprocessor 8085 • 225 questions available
About 10. Programmable Keyboard and Display Interface: 8279
Think about how a calculator or a microwave keypad works. The CPU can't just keep checking all the keys to see if one is pressed—that would waste a lot of time. The 8279 is a special-purpose chip designed specifically to manage a matrix of keys (a keyboard) and a set of 7-segment displays. It acts as a dedicated "manager" that automatically scans the keyboard, debounces the key presses (cleans up the electrical noise), and stores the key code in its own memory for the CPU to read whenever it's ready.
How It Works: The 8279 has two main sections: one for the keyboard and one for the display. For the keyboard, you set up which keys are in the matrix. The chip scans the rows and columns of the keyboard, and when a key is pressed, it debounces it and puts the key code into a FIFO (First-In, First-Out) RAM. For the display, the CPU simply sends the data it wants to show to the 8279, and the chip automatically refreshes the display (updates the segments) continuously, so the CPU doesn't have to do it. This is called "display scanning."
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🔄 Last updated: 2026-07-30