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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Sl outputs are active-high, follow binary bit pattern or Z selects auto-increment so subsequent writes go to subsequent display positions. SL outputs are active-low only one low at any time. In the keyboard mode, this line is used as a control input and stored in FIFO on a key closure.

In the Interrupt modethe processor is requested service only if any key is pressed, otherwise the CPU will continue with its main task. Strobed keyboard, decoded display scan. These lines can be programmed as encoded or decoded, using the mode control register.

The output lines can 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. In encoded scan mode, the output of scan lines will be binary count, and so an external decoder should be used to convert the binary count to decoded output. It has an internal pull up. Consists of bi-directional pins that connect to data bus on micro.


Keyboard Interface of First three bits given below select one of 8 control registers opcode. Programs internal clk, sets scan and debounce times. Causes DRAM memory system to be refreshed.

In decoded scan mode, the output of scan lines will be similar to a 2-to-4 decoder. SL outputs are active-high, follow binary bit pattern or depending on 8 or 16 digit display. These lines are set to 0 when any key is pressed. BB works similarly except controllef they blank turn off half of the output pins.

Microprocessor – Programmable Keyboard

Scan line outputs scan both the keyboard and displays. RL pins incorporate internal pull-ups, no need for external resistor pull-ups. The status of the shift key and control key are also stored along with key code. The output lines are connected to the anodes through driver transistor in case of common cathode 7-segment LEDs.

Decoded keyboard with N-key rollover. Output keyboarr blanks the displays. DD Function 00 8-digit display with left entry 01 digit display with left entry 879 8-digit display with right entry 11 digit display with right entry.


When it is low, it indicates the transfer of data. The display section consists of 16 x 8 display RAM.

8279 – Programmable Keyboard

The timing and control unit handles the timings for the operation of the circuit. Interrupt request, becomes 1 when a key is pressed, data is available.

Output that blanks the displays. It has two additional input: In the encoded mode, the counter provides the binary count that is to be externally decoded controllet provide the scan lines for the keyboard and display. The scans RL pins synchronously with the scan.

Programmable Keyboard/Display Interface –

The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts. This unit controls the flow of data through the microprocessor. About project SlidePlayer Terms of Service. The scan lines are common for keyboard and display. Encoded mode and Decoded mode. In the scanned sensor matrix mode, this unit acts as sensor RAM where its each row is loaded with the status of their corresponding row of sensors into the kfyboard.