1205 Ppi 8279
- 1. Programmable Keyboard/Display Interface THE 8279
- 2. Block diagram of 8279 based system 8085 8279 16-character Display 16-Key Matrix Keyboard Keyboard Control Decoder SL0 SL1 SL2 SL3 BD A3-A0 B3-B0 RL3-RL0 D7-D0 RD WR IRQ CLK A0
- 3. Introduction 8279 A programmable keyboard and display interfacing chip Hardware approach to interfacing a matrix keyboard and a multiplexed display Scans and encodes up to 64-key keyboard Controls up to 16-digit numerical display
- 4. 8279 has 4 main segments Keyboard Scan Display MPU Interface
- 5. 1. Keyboard Section Consists of 8 lines (RL0-RL7) that can be connected to eight columns of a matrix keyboard Shift and CNTL/STB (Control/Strobe) 8-byte FIFO RAM Keys are automatically debounced
- 6. Block Diagram 8279 Keyboard Section
- 7. 2. Display Section Consists of 8 output lines (A0-A3) and (B0-B3) 16 byte display RAM BD line used to blank displays
- 8. Block Diagram 8279 Display Section
- 9. 3. Scan Section Consists of Scan Counter Four scan lines (SL0-SL3) Used by keyboard and display section for proper functioning
- 10. Block Diagram 8279 Scan Section
- 11. MPU Interface section 8 bidirectional data lines (DB0-DB7) IRQ line RD line WR line CS line RESET line Buffer address line (A0)
- 12. Block Diagram 8279 MPU Interface Section
- 13. Pin Description 8279 A0: Selects data (0) or control/status (1) for reads and writes between micro and 8279. Output that blanks the displays. CLK: Used internally for timing. Max is 3 MHz. CN/ST: Control/strobe, connected to the control key on the keyboard. Chip select that enables programming, reading the keyboard, etc . DB7-DB0: Consists of bi-directional pins that connect to data bus on micro .
- 14. IRQ: Interrupt request, becomes 1 when a key is pressed, data is available. OUT A3-A0/B3-B0: Outputs that sends data to the most significant/least significant nibble of display. : Connects to micro's IORC or RD signal, reads data/status registers. RESET: Connects to system RESET. RL7-RL0: Return lines are inputs used to sense key depression in the keyboard matrix. Shift: Shift connects to Shift key on keyboard. SL3-SL0: Scan line outputs scan both the keyboard and displays.
- 15. Scanning keys of a Matrix Keyboard Vcc Row0 Row1 Row2 Row3 C0 C1 C2 C3 R = 4.7K R = 4.7K 0 1 2 3 4 5 6 7 8 9 A B C D E F
- 16. Connecting a 7-segment display with 8279 8279 4-to-16 decoder SL0 SL1 SL2 SL3 A0 A1 A2 A3 B0 B1 B2 B3 a b c d e f g h O 15 O 0 V CC a b c d e f g h V CC O 1
- 17. Working with a multiplexed display 8279 4-to-16 decoder SL0 SL1 SL2 SL3 A0 A1 A2 A3 B0 B1 B2 B3 O 15 O 0 T1 O 1 T2 O 2 T3 O 3 T4
- 18. Connecting a 64-key Keyboard with 8279 8279 4-to-16 decoder SL0 SL1 SL2 SL3 RL0 O 13 O 0 O 7 Multiplexed 7-Segment Display O 8 O 9 O 10 O 11 O 12 O 14 O 15 RL1 RL2 RL3 RL4 RL5 RL6 RL7