Programmable Keyboard/Display Interface – A programmable keyboard and display interfacing chip. Scans and encodes up to a key keyboard. All data and commands between the CPU and the programmable keyboard interface are transferred on these lines. CLK (Clock) Generally, a system clock. User Manual for Keyboard and Display Interface Card. Hardware Configuration of With // 50 PIN HEADER. CONNECTIONS.

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Interrupt request, becomes 1 when a key is pressed, data is available. Conditional Statement in Assembly Language Program. When it is low, it indicates the transfer of data. It then sends their relative response of the pressed key to the CPU and vice-a-versa. Memory Interfacing in Scan line outputs scan both the keyboard and displays. There are 6 modes of operation for each counter: Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8.


Operating Modes of Interface of Code given in text for reading keyboard. Interfacing of with The timing and control unit handles the timings for the operation of the circuit.

The previous example illustrates an encoded keyboard, external itnerfacing used to drive matrix. Pinout Definition A0: MMM sets keyboard mode.

Selects type of FIFO read and address of the read. Provides a timing source to the internal speaker and other devices.

To determine if a character has been typed, the FIFO status register is checked. 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 display read and address of the read.

The keyboard consists of maximum 64 keys, which are interfaced with the CPU by using the key-codes. Z selects auto-increment for the address.

Strobed keyboard, encoded display scan. If more than 8 characters are entered in the FIFO, then it means interfaccing than eight keys are pressed at a time.


Microprocessor – Programmable Keyboard

Encoded mode and Decoded mode. CLK input of is driven from the clock out of DD field selects either: Used for controlling real-time events such as real-time clock, events counter, and motor speed and direction control.

Generates a continuous square-wave with G set to 1. A 0 signal from the is connected to the A 0 input of Keyboard Interface of This mode is further classified into two output modes.

8279 – Programmable Keyboard

The first 3 bits of sent to control port selects one of 8 control words. Encoded keyboard with N-key rollover.

Selects type of write and the address of the write. This mode deals with display-related operations. Used internally for timing.