Programmable Programmable Keyboard/Display Interface - Keyboard/Display Interface -

82798279

8279 contains the following features:8279 contains the following features: Simultaneous and independent scanning of a keyboard and Simultaneous and independent scanning of a keyboard and

refresh of a display,refresh of a display, significantly offloading these functions from the significantly offloading these functions from the

microprocessor.microprocessor.Keyboard section:Keyboard section: 8-character Keyboard FIFO8-character Keyboard FIFO 2-Key Lockout or N-key Rollover with Contact Debounce2-Key Lockout or N-key Rollover with Contact Debounce Interrupt Output on Key EntryInterrupt Output on Key Entry Programmable Keyboard Scan & Debounce ratesProgrammable Keyboard Scan & Debounce rates

Display Section:Display Section: Dual 8- or 16-Numeric DisplayDual 8- or 16-Numeric Display Single 16-Character DisplaySingle 16-Character Display Right or Left Entry 16-Byte Display RAM with address auto incrementRight or Left Entry 16-Byte Display RAM with address auto increment Programmable display refresh rateProgrammable display refresh rate

Available in VHDL, Verilog, or FPGA-Specific Available in VHDL, Verilog, or FPGA-Specific NetlistNetlist

PIN DIAGRAMPIN DIAGRAM

Pinout Definition 8279Pinout Definition 8279 P A0: Selects data (0) or control/status (1) for reads and P A0: Selects data (0) or control/status (1) for reads and

writes between micro and 8279.writes between micro and 8279. P BD: Output that blanks the displays.P BD: Output that blanks the displays. P CLK: Used internally for timing. Max is 3 MHz.P CLK: Used internally for timing. Max is 3 MHz. P CN/ST: Control/strobe, connected to the control key on P CN/ST: Control/strobe, connected to the control key on

the keyboard.the keyboard. P CS: Chip select that enables programming, reading the keyboard, etc.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 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 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 P OUT A3-A0/B3-B0: Outputs that sends data to the most significant/least

significant nibble of display.significant nibble of display. P RD(WR): Connects to micro's IORC or RD signal, reads data/status registers.P RD(WR): Connects to micro's IORC or RD signal, reads data/status registers. P RESET: Connects to system RESET.P RESET: Connects to system RESET. P RL7-RL0: Return lines are inputs used to sense key depression in the keyboard P RL7-RL0: Return lines are inputs used to sense key depression in the keyboard

matrix.matrix. P Shift: Shift connects to Shift key on keyboard.P Shift: Shift connects to Shift key on keyboard. P SL3-SL0: Scan line outputs scan both the keyboard and displaysP SL3-SL0: Scan line outputs scan both the keyboard and displays

KEYBOARD SECTIONKEYBOARD SECTION

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

2 modes:2 modes: 2 key lockout: if two keys are pressed simultaneously only 12 key lockout: if two keys are pressed simultaneously only 1stst key key

is recognizedis recognized N-key rollover: simultaneous keys are recognized and their codes N-key rollover: simultaneous keys are recognized and their codes

are stored in internal buffer.are stored in internal buffer.

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

SCAN SECTIONSCAN SECTION

Has scan counter and four scan lines: SL0 to Has scan counter and four scan lines: SL0 to SL3SL3

These are decoded using 4X16 decoderThese are decoded using 4X16 decoder Further these 16 lines are connected to rows of Further these 16 lines are connected to rows of

matrix keyboard and digital drivers of matrix keyboard and digital drivers of multiplexed displaymultiplexed display

DISPLAY SECTIONDISPLAY SECTION

Has 8 output lines divided into 2 groups A0 to Has 8 output lines divided into 2 groups A0 to A3 and B0 to B3A3 and B0 to B3

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

Display can be blanked by BD lineDisplay can be blanked by BD line Includes 16X8 display RAMIncludes 16X8 display RAM MPU can read or write into these registersMPU can read or write into these registers

MPU INTERFACE SECTIONMPU INTERFACE SECTION

Includes 8 bidir. Data lines (DB0-DB7), one Includes 8 bidir. Data lines (DB0-DB7), one Interrupt Request (IRQ) and six lines for Interrupt Request (IRQ) and six lines for interfacing, including buffer add line A0interfacing, including buffer add line A0

When A0 is high – control wordWhen A0 is high – control word When A0 is low – signals are interrupted and When A0 is low – signals are interrupted and

they act as data linesthey act as data lines IRQ goes high whenever data entries are IRQ goes high whenever data entries are

stored in FIFOstored in FIFO