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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When it is low, it indicates the transfer of data.

Programmable Keyboard/Display Interface –

Selects type of display read and address of the read. BB works similarly except that they blank turn off half of the output pins. Interrupts the micro at interrupt vector 8 for a clock tick. 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.

Clears the IRQ signal to the microprocessor. Shift connects to Shift key on keyboard.

The Shift input line status is stored along with every key code in FIFO in the scanned keyboard mode. Z selects auto-increment for the address. Encoded keyboard with 2-key lockout.


8279 – Programmable Keyboard

An events counter enabled with G. Programmmable has two modes i. This mode deals with display-related operations. These lines are set to 0 when any key is pressed. Selects type of FIFO read and address of the read.

Generates a continuous square-wave with G set to 1.

Consists of bidirectional pins that connect to data bus on micro. If more than 8 characters are entered in the FIFO, then it means more than eight keys are pressed at a time. There are 6 modes of operation for each counter: Usually decoded at port address 40HH and has following functions: Encoded mode and Decoded mode.

The output becomes a logic 0 when the control word is written and remains there until N plus the number of programmed counts. Decoded keyboard with N-key rollover. Generates a basic timer interrupt that interace at approximately Output that blanks the displays.

Keyboard has a built-in FIFO 8 character buffer. Used internally for timing. Decoded keyboard dsplay 2-key lockout. It is enabled only when D is low. The first 3 bits of sent to control port selects one of 8 control words. Keyboard Interface of The display is controlled from an internal 16×8 RAM that stores the coded display information. 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. In the encoded mode, the counter provides programjable binary count that is to be externally decoded to provide the scan lines for the keyboard and display. Allows half-bytes to be blanked. Clears the display or FIFO. This is when the overrun status is set. The scans RL pins synchronously with the scan.

In the scanned sensor matrix mode, this unit acts as sensor RAM where its each programmabe is loaded with the status of their proggammable row of sensors into the interfwce. Chip select that enables programming, reading the keyboard, etc. Counter reloaded if G is pulsed again. These lines can be programmed as encoded or decoded, using the mode control register.

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