Programmable Keyboard/Display Interface - 8279

1. Programmable Keyboard/Display Interface - 8279

3. 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.

4. 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

5. 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

6. 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