Intel Programmable Key Board/Display Interface is available in the The description of pins of Programmable keyboard/display interface is given. The INTEL is specially developed for interfacing keyboard and display devices Programmable scan timing. Block diagram of The four major sections of are keyboard, scan, display and CPU interface. Keyboard section. The INTEL is a Keyboard/Display Controller specially developed for interfacing keyboard Programmable scan timing. Keyboard section: The CPU interface section takes care of data transfer between the and the processor.

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8279 – Programmable Keyboard

Decoded keyboard with 2-key lockout. To determine if a character has been typed, the FIFO status register is checked. Used internally for timing. The keyboard consists of maximum 64 keys, which are interfaced with the CPU by using the key-codes.

MMM sets keyboard mode. Scan line outputs scan both the keyboard and displays. Clears the IRQ signal to the microprocessor. These are the output ports for two 16×4 or one 16×8 internal display refresh dispplay.

DD sets displays mode.

Programmable Keyboard/Display Interface –

Keyboard has a built-in FIFO 8 character buffer. The scans RL pins synchronously with the scan.


Programs internal clk, innterface scan and debounce times. Generates a basic timer interrupt that occurs at approximately The display is controlled from an internal 16×8 RAM that stores the coded display information. The 74LS drives 0’s on one line at a time.

Interface of WWBB The display write inhibit control word inhibits writing to either the leftmost 4 bits of the display left W or rightmost 4 bits. The data from these lines is synchronized with the scan lines to scan the display and the keyboard. The Keyboard can be interfaced either in the interrupt or the polled mode.

If two bytes are programmed, then the first byte LSB stops the count, and the second byte MSB starts the counter with the new count. The line is pulled down with a key closure.

Intel 8279

Minimum count is 1 all modes except 2 and 3 with programable count of 2. Sl outputs are active-high, follow binary bit pattern or In the Polled modethe CPU periodically reads an internal flag of to check idsplay any key is pressed or not with key pressure. Selects type of FIFO read and address of the read. These lines are set to 0 when any key is pressed. In the encoded mode, the counter provides the binary count that is to be externally decoded to provide the scan lines for the keyboard and display.


Unlike the 82C55, the must be programmed first. Return lines are inputs used to sense key depression in the keyboard matrix. Encoded mode and Decoded mode.

Used for controlling real-time events such as real-time clock, events counter, keyboaard motor speed and direction control. This is when the overrun status is set. Interface of Code given in text for reading keyboard. If more than 8 characters are entered in the FIFO, then it means more than eight keys are pressed at a time. Encoded keyboard with N-key rollover. The keyboard first scans the keyboard and identifies if any key has been pressed.

Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8. The Shift input line status is stored along with every key code in FIFO in the scanned keyboard mode.