Programmable Keyboard/Display Interface

8279 contains the following features: Simultaneous and independent scanning of a keyboard and refresh of a display, Simultaneous and independent scanning of a keyboard and refresh of a display, significantly offloading these functions from the microprocessor. significantly offloading these functions from the microprocessor. Keyboard section: 8-character Keyboard FIFO 8-character Keyboard FIFO 2-Key Lockout or N-key Rollover with Contact Debounce 2-Key Lockout or N-key Rollover with Contact Debounce Interrupt Output on Key Entry Interrupt Output on Key Entry Programmable Keyboard Scan & Debounce rates Programmable Keyboard Scan & Debounce rates Display Section: Dual 8- or 16-Numeric Display Dual 8- or 16-Numeric Display Single 16-Character Display Single 16-Character Display Right or Left Entry 16-Byte Display RAM with address auto increment Right or Left Entry 16-Byte Display RAM with address auto increment Programmable display refresh rate Programmable display refresh rate Available in VHDL, Verilog, or FPGA-Specific Netlist

PIN DIAGRAM

Pinout 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 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. 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 significant nibble of display. 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 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 matrix. 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 Shift: Shift connects to Shift key on keyboard. P SL3-SL0: Scan line outputs scan both the keyboard and displays P SL3-SL0: Scan line outputs scan both the keyboard and displays

KEYBOARD SECTION Has eight lines: RL0 to RL7 + two additional lines: CNTL/STB; connected to 8 columns of the keyboard Has eight lines: RL0 to RL7 + two additional lines: CNTL/STB; connected to 8 columns of the keyboard 2 modes: 2 modes: 2 key lockout: if two keys are pressed simultaneously only 1 st key is recognized 2 key lockout: if two keys are pressed simultaneously only 1 st key is recognized N-key rollover: simultaneous keys are recognized and their codes are stored in internal buffer. 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. Keyboard section also includes 8X8 FIFO which further consists of eight registers that can store 8 keyboard entries.

SCAN SECTION Has scan counter and four scan lines: SL0 to SL3 Has scan counter and four scan lines: SL0 to SL3 These are decoded using 4X16 decoder These are decoded using 4X16 decoder Further these 16 lines are connected to rows of matrix keyboard and digital drivers of multiplexed display Further these 16 lines are connected to rows of matrix keyboard and digital drivers of multiplexed display

DISPLAY SECTION Has 8 output lines divided into 2 groups A0 to A3 and B0 to B3 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 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 Display can be blanked by BD line Includes 16X8 display RAM Includes 16X8 display RAM MPU can read or write into these registers MPU can read or write into these registers

MPU INTERFACE SECTION Includes 8 bidir. Data lines (DB0-DB7), one Interrupt Request (IRQ) and six lines for interfacing, including buffer add line A0 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 high – control word When A0 is low – signals are interrupted and they act as data lines When A0 is low – signals are interrupted and they act as data lines IRQ goes high whenever data entries are stored in FIFO IRQ goes high whenever data entries are stored in FIFO