1205 Ppi 8279


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1205 Ppi 8279

  1. 1. Programmable Keyboard/Display Interface THE 8279
  2. 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. 3. Introduction 8279 <ul><li>A programmable keyboard and display interfacing chip </li></ul><ul><li>Hardware approach to interfacing a matrix keyboard and a multiplexed display </li></ul><ul><li>Scans and encodes up to 64-key keyboard </li></ul><ul><li>Controls up to 16-digit numerical display </li></ul>
  4. 4. <ul><li>8279 has 4 main segments </li></ul><ul><ul><li>Keyboard </li></ul></ul><ul><ul><li>Scan </li></ul></ul><ul><ul><li>Display </li></ul></ul><ul><ul><li>MPU Interface </li></ul></ul>
  5. 5. 1. Keyboard Section <ul><li>Consists of </li></ul><ul><ul><li>8 lines (RL0-RL7) that can be connected to eight columns of a matrix keyboard </li></ul></ul><ul><ul><li>Shift and CNTL/STB (Control/Strobe) </li></ul></ul><ul><ul><li>8-byte FIFO RAM </li></ul></ul><ul><li>Keys are automatically debounced </li></ul>
  6. 6. Block Diagram 8279 Keyboard Section
  7. 7. 2. Display Section <ul><li>Consists of </li></ul><ul><ul><li>8 output lines (A0-A3) and (B0-B3) </li></ul></ul><ul><ul><li>16 byte display RAM </li></ul></ul><ul><ul><li>BD line used to blank displays </li></ul></ul>
  8. 8. Block Diagram 8279 Display Section
  9. 9. 3. Scan Section <ul><li>Consists of </li></ul><ul><ul><li>Scan Counter </li></ul></ul><ul><ul><li>Four scan lines (SL0-SL3) </li></ul></ul><ul><li>Used by keyboard and display section for proper functioning </li></ul>
  10. 10. Block Diagram 8279 Scan Section
  11. 11. MPU Interface section <ul><li>8 bidirectional data lines (DB0-DB7) </li></ul><ul><li>IRQ line </li></ul><ul><li>RD line </li></ul><ul><li>WR line </li></ul><ul><li>CS line </li></ul><ul><li>RESET line </li></ul><ul><li>Buffer address line (A0) </li></ul>
  12. 12. Block Diagram 8279 MPU Interface Section
  13. 13. Pin Description 8279 <ul><li>A0: Selects data (0) or control/status (1) for reads and writes between micro and 8279. </li></ul>Output that blanks the displays. <ul><li>CLK: Used internally for timing. Max is 3 MHz. </li></ul><ul><li>CN/ST: Control/strobe, connected to the control key on the keyboard. </li></ul><ul><li>Chip select that enables programming, reading the keyboard, etc . </li></ul><ul><li> DB7-DB0: Consists of bi-directional pins that connect to data bus on micro . </li></ul>
  14. 14. <ul><li>IRQ: Interrupt request, becomes 1 when a key is pressed, data is available. </li></ul><ul><li>OUT A3-A0/B3-B0: Outputs that sends data to the most significant/least significant nibble of display. </li></ul><ul><li>: Connects to micro's IORC or RD signal, reads data/status registers. </li></ul><ul><li>RESET: Connects to system RESET. </li></ul><ul><li>RL7-RL0: Return lines are inputs used to sense key depression in the keyboard matrix. </li></ul><ul><li>Shift: Shift connects to Shift key on keyboard. </li></ul><ul><li>SL3-SL0: Scan line outputs scan both the keyboard and displays. </li></ul>
  15. 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. 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. 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. 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