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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Selects type of display read and address of the read.

DD sets displays mode. RL pins incorporate internal pull-ups, no need for external resistor pull-ups. The address inputs select one of the four internal registers with the as follows: 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 scans RL pins synchronously with the scan. Selects type of FIFO read and address of the read.

Controls up to a digit numerical display. Keyboard Interface of Keyboard Interface of First three bits given below select one of 8 control registers opcode.


Programmable Keyboard/Display Interface –

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. It is enabled only when D is low. Keyboard Interface of The keyboard matrix can be any size from 2×2 to 8×8.

Programs internal clk, sets scan and debounce times. Generates a continuous square-wave with G set to 1. These are the Return Lines which are connected to one terminal of keys, while the other terminal of the keys is connected to the decoded scan lines.

Encoded keyboard with 2-key lockout. If more than 8 characters are entered in the FIFO, then it means more than eight keys are pressed at a time. Shift connects to Keyboxrd key on keyboard. This mode deals with the input given by the keyboard and this mode is further classified into 3 modes.

These are the scan lines used programmable scan the keyboard matrix and display the digits. Clears the display or FIFO.

Microprocessor – Programmable Keyboard

Scans and encodes up to a key keyboard. Minimum count is 1 all modes except 2 and 3 with minimum count of 2. BB works similarly except that they blank turn off half of the output pins.

Selects type of write and the address of the write. Keyboard has a built-in FIFO 8 character buffer.

The 74LS drives 0’s on one line at a time. Once done, a procedure is needed to read data from the keyboard. The data from interfqce lines is synchronized with the scan lines to scan the display and the keyboard. In the keyboard mode, this line is used as a control input and stored in FIFO on a key closure. Interface of Code given in text for reading keyboard.


It has an internal pull up. Generates a basic timer interrupt that occurs at approximately This unit contains registers to store the keyboard, display modes, displxy other operations as programmed by the CPU. Pinout Definition A0: The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts.

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

8279 – Programmable Keyboard

DD field selects either: The previous example illustrates an encoded keyboard, external decoder used to drive matrix. Decoded keyboard with N-key rollover. Xisplay mode deals with display-related operations. 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.