Programmable keyboard display interface 8279
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Programmable Keyboard/Display Interface - 8279. 8279 contains the following features:. Simultaneous and independent scanning of a keyboard and refresh of a display, significantly offloading these functions from the microprocessor. Keyboard section: 8-character Keyboard FIFO

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Programmable Keyboard/Display Interface - 8279

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Programmable keyboard display interface 8279

Programmable Keyboard/Display Interface - 8279


8279 contains the following features

8279 contains the following features:

  • Simultaneous and independent scanning of a keyboard and refresh of a display,

  • significantly offloading these functions from the microprocessor.

    Keyboard section:

    • 8-character Keyboard FIFO

    • 2-Key Lockout or N-key Rollover with Contact Debounce

    • Interrupt Output on Key Entry

    • Programmable Keyboard Scan & Debounce rates

      Display Section:

    • Dual 8- or 16-Numeric Display

    • Single 16-Character Display

    • Right or Left Entry 16-Byte Display RAM with address auto increment

    • Programmable display refresh rate

      Available in VHDL, Verilog, or FPGA-Specific Netlist


Pin diagram

PIN DIAGRAM


Pinout definition 8279

Pinout Definition 8279

  • P A0: Selects data (0) or control/status (1) for reads and

    writes between micro and 8279.

  • P BD: Output that blanks the displays.

  • P CLK: Used internally for timing. Max is 3 MHz.

  • P CN/ST: Control/strobe, connected to the control key on

    the keyboard.

  • P CS: Chip select that enables programming, reading the keyboard, etc.

  • P DB7-DB0: Consists of bidirectional pins that connect to data bus on micro.

  • P IRQ: Interrupt request, becomes 1 when a key is pressed, data is available.

  • P OUT A3-A0/B3-B0: Outputs that sends data to the most significant/least significant nibble of display.

  • P RD(WR): Connects to micro's IORC or RD signal, reads data/status registers.

  • P RESET: Connects to system RESET.

  • P RL7-RL0: Return lines are inputs used to sense key depression in the keyboard matrix.

  • P Shift: Shift connects to Shift key on keyboard.

  • P SL3-SL0: Scan line outputs scan both the keyboard and displays


Keyboard section

KEYBOARD SECTION

  • Has eight lines: RL0 to RL7 + two additional lines: CNTL/STB; connected to 8 columns of the keyboard

  • 2 modes:

    • 2 key lockout: if two keys are pressed simultaneously only 1st key is recognized

    • N-key rollover: simultaneous keys are recognized and their codes are stored in internal buffer.

  • Keyboard section also includes 8X8 FIFO which further consists of eight registers that can store 8 keyboard entries.


  • Scan section

    SCAN SECTION

    • Has scan counter and four scan lines: SL0 to SL3

    • These are decoded using 4X16 decoder

    • Further these 16 lines are connected to rows of matrix keyboard and digital drivers of multiplexed display


    Display section

    DISPLAY SECTION

    • Has 8 output lines divided into 2 groups A0 to A3 and B0 to B3

    • These lines can be used as a group of 8 lines or 2 groups of 4 lines each in conjunction to scan lines for display

    • Display can be blanked by BD line

    • Includes 16X8 display RAM

    • MPU can read or write into these registers


    Mpu interface section

    MPU INTERFACE SECTION

    • Includes 8 bidir. Data lines (DB0-DB7), one Interrupt Request (IRQ) and six lines for interfacing, including buffer add line A0

    • When A0 is high – control word

    • When A0 is low – signals are interrupted and they act as data lines

    • IRQ goes high whenever data entries are stored in FIFO


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