1. © 2000 Morgan Kaufman Overheads for Computers as Components The Embedded computing platform zCPU bus. zMemory. zI/O devices.

2. © 2000 Morgan Kaufman Overheads for Computers as Components CPU bus zConnects CPU to: ymemory; ydevices. zProtocol controls communication between entities.

3. © 2000 Morgan Kaufman Overheads for Computers as Components Bus protocol zDetermines who gets to use the bus at any particular time. zGoverns length, style of communication.

4. © 2000 Morgan Kaufman Overheads for Computers as Components Four-cycle handshake zBasis of many bus protocols. zUses two wires: yenq (enquiry); yack (acknowledgment). dev1dev2 enq ack data

5. © 2000 Morgan Kaufman Overheads for Computers as Components Four-cycle example time enq ack data 1 2 3 4

6. © 2000 Morgan Kaufman Overheads for Computers as Components Typical bus signals zClock. zR/W’: true when bus is reading. zAddress: a-bit bundle. zData: n-bit bundle. zData ready’.

7. © 2000 Morgan Kaufman Overheads for Computers as Components Timing diagrams time A B C zero one rising falling stable changing 10 ns

8. © 2000 Morgan Kaufman Overheads for Computers as Components Typical bus timing for read zCPU: yset R/W’=1; yasserts address, address enable. zMemory: yasserts data; yasserts data ready’. zCPU: ydeasserts address, address enable.

9. © 2000 Morgan Kaufman Overheads for Computers as Components Bus read state diagram Get data Done Adrs Wait See ack

10. © 2000 Morgan Kaufman Overheads for Computers as Components Transaction types zWait state: ystate in a bus transaction to wait for acknowledgment. zDisconnected transfer: ybus is freed during wait state. zBurst: ymultiple transfers.

11. © 2000 Morgan Kaufman Overheads for Computers as Components Timers and counters zVery similar: ya timer is incremented by a periodic signal; ya counter is incremented by an asynchronous, occasional signal. zRollover causes interrupt.

12. © 2000 Morgan Kaufman Overheads for Computers as Components Watchdog timer zWatchdog timer is periodically reset by system timer. zIf watchdog is not reset, it generates an interrupt to reset the host. host CPU watchdog timer interrupt reset

13. © 2000 Morgan Kaufman Overheads for Computers as Components Switch debouncing zA switch must be debounced to multiple contacts caused by eliminate mechanical bouncing:

14. © 2000 Morgan Kaufman Overheads for Computers as Components Encoded keyboard zAn array of switches is read by an encoder. zN-key rollover remembers multiple key depressions. row

15. © 2000 Morgan Kaufman Overheads for Computers as Components LED zMust use resistor to limit current:

16. © 2000 Morgan Kaufman Overheads for Computers as Components 7-segment LCD display zMay use parallel or multiplexed input.

17. © 2000 Morgan Kaufman Overheads for Computers as Components Types of high-resolution display zCathode ray tube (CRT) zLiquid crystal display (LCD) zPlasma, etc.

18. © 2000 Morgan Kaufman Overheads for Computers as Components Touchscreen zIncludes input and output device. zInput device is a two-dimensional voltmeter:

19. © 2000 Morgan Kaufman Overheads for Computers as Components Touchscreen position sensing ADC voltage

20. © 2000 Morgan Kaufman Overheads for Computers as Components Digital-to-analog conversion zUse resistor tree: R 2R 4R 8R bnbn b n-1 b n-2 b n-3 V out

21. © 2000 Morgan Kaufman Overheads for Computers as Components Flash A/D conversion zN-bit result requires 2 n comparators: encoder V in...

22. © 2000 Morgan Kaufman Overheads for Computers as Components Dual-slope conversion zUse counter to time required to charge/discharge capacitor. zCharging, then discharging eliminates non-linearities. V in timer

23. © 2000 Morgan Kaufman Overheads for Computers as Components Sample-and-hold zRequired in any A/D: converter V in