Intel’s is a general purpose Keyboard Display controller that simultaneously drives the display of a system and interfaces a Keyboard with the CPU. The Keyboard Display interface scans the Keyboard to identify if any key has been In the Polled mode, the CPU periodically reads an internal flag of to . KEYBOARD/DISPLAY CONTROLLER – INTEL Features of The important features of are, Simultaneous keyboard and display operations.

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Z selects auto-increment so subsequent writes go to subsequent display positions.

Generates a basic timer interrupt that occurs at approximately This unit controls the flow of data through the microprocessor. Used internally for timing. Six Digit Display Interface of DD Function 00 8-digit display with left entry 01 digit display with left entry 10 8-digit display with right entry 11 digit display with right entry. MMM sets keyboard mode.

Programmable Keyboard/Display Interface –

These lines are set to 0 when any key comtroller pressed. Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8. Scan line outputs scan both the keyboard and displays. The Shift input line status is stored along with every key code in FIFO in the scanned keyboard mode. Registration Forgot your password?

8279 – Programmable Keyboard

Used internally for keyboad. Chip select that enables programming, reading the keyboard, etc. Selects type of display read and address of the read. MMM sets keyboard mode. The address inputs select one of the four internal registers with the as follows: Causes DRAM memory system to be refreshed. BB works similarly except that they blank turn off half of the output pins. Strobed keyboard, decoded display scan. Counter reloaded if G is pulsed again.


The cathodes are connected to scan lines through driver transistors.

Intel 8279

DD sets displays mode. SL outputs are active-low only one of the four outputs will be low at any time.

Encoded keyboard with 2-key lockout. Shift connects to Shift key on keyboard. This unit contains registers to store the keyboard, display ieyboard, and other operations as programmed by the CPU.

Clears the display or FIFO. DD field selects either: Usually decoded at port address 40HH and has following functions: The Keyboard can be interfaced contdoller in the interrupt or the polled mode.

The output lines ,eyboard be used either as a single group of eight lines or as two groups of four lines, in conjunction with the scan lines for a multiplexed display. Z selects auto-increment for the address. There are 6 modes of operation for each counter: In the Polled modediisplay CPU periodically reads an internal flag of to check whether any key is pressed or not with key pressure.

In the decoded scan modethe counter internally decodes the least significant 2 bits and provides a decoded 1 out of 4 scan on SL 0 -SL 3. Selects type of FIFO read and address of the read. These are the output ports for two 16×4 or one 16×8 internal display refresh registers.

Interrupts the micro at interrupt vector 8 for a clock tick.


Microprocessor – Programmable Keyboard

To use this website, you must agree to our Privacy Policyincluding cookie policy. The keyboard consists of maximum 64 keys, which are interfaced with the CPU dislay using the key-codes. Once done, a procedure is needed to read data from the keyboard. Interface of 2 Keyboard type is programmed next.

It has two modes i. DD Function Encoded keyboard with 2-key lockout Decoded keyboard with 2-key lockout Encoded keyboard with N-key rollover Decoded keyboard with N-key rollover Encoded sensor matrix Decoded sensor matrix Strobed keyboard, encoded display scan Strobed keyboard, decoded display scan Encoded: The display section consists of 16 x 8 display RAM.

Pins SL2-SL0 sequentially scan each column through a counting operation. Unlike the 82C55, the must be programmed first. Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control. Consists of bi-directional pins that connect to data bus on micro.

Interrupt request, becomes 1 when a displya is pressed, data is available. We think you have liked this presentation.

Feedback Privacy Policy Feedback. Minimum count is 1 all modes except 2 and 3 with minimum count of 2. Return lines are inputs used to sense key depression in the keyboard matrix. If more than 8 characters are entered in the FIFO, then it means more than eight keys are pressed at a time.