ECE 353 Introduction to Microprocessor Systems

1. ECE 353Introduction to Microprocessor Systems Michael Schulte Week 7

2. Administrative Matters • Homework #4 is due Friday, April 4th, 2008 • Quiz #2 is rescheduled for Thursday, April 10th from 7:15 to 8:30 • Discussion section tonight 6:30-8:00pm in 3534 Engineering Hall • Memory Maps and Address Decoding • Reading for week8 • ADuC702X Datasheet 53-60, 71-73, 75-79

3. Topics • Microprocessor support circuits • Clock and reset generation • Power control • Microprocessor supervisors • I/O subsystems • GPIO pin construction • I/O port design • I/O decoding • I/O synchronization • ADuC7026 GPIO

4. ADuC7026 Block Diagram

5. Clocks • Clock Generation • Clock oscillators • External clocks • Phase-locked loops (PLLs) • Operation and design issues • ADuC7026 clocking • PLLCON • Power Control • ADuC7026 operating modes • POWCON ADuC7026 pin-out

6. Reset • The reset signal is used to force the processor into a known state from which operation can reliably be started. • On power up, the reset signal should be asserted long enough to ensure that the supply voltages are stable and the oscillator is running and stable • Reset Generation • RC reset circuit operation • Shortcomings ADuC7026 pin-out

7. Microprocessor Supervisors • Microprocessor supervisors provide reset functionality for a variety of circumstances • Power-up • Brown-out • Glitches • They can also provide a number of other services • MAX807 ADuC7026 pin-out

8. Basic System Bus Operation • Address • Unidirectional from CPU • Data • Bidirectional • Control • /RS or /RD – output from CPU • Indicates a read operation in progress • /WS or /WR – output from CPU • Indicates a write operation in progress • /WAIT or /READY – input to CPU • Used by external device to signal that it is not able to complete transfer yet • Read/Write Sequence

9. I/O Port Basics • I/O subsystems allow the CPU to interact with the outside world • Basic GPIO pin requirements • Configurable as input or output • Can set value driven out on the pin • Can read the current value on the pin • Configurable vs. multiplexed pins • Unconditional I/O • The I/O device can accept or return data without delay ADuC7026 pin-out

10. MSI I/O Ports • Medium Scale Integration (MSI) circuits are available to construct ports • Simple byte input ports can be constructed from… • Octal buffers • Octal registers • Simple byte output ports can be constructed from octal registers

11. P Compatible I/O Devices • Complex I/O devices typically require more sophisticated interface and control logic • P compatible I/O devices have the necessary logic built in to the device itself • Interface designed to be reasonably compatible with many microprocessor buses • Need to add decoding/selection logic • Example • Device controllers • An organizational model commonly used to interface to complex I/O devices (serial ports, LCDs, disk drives, etc.) • Generic model • Example – Hitachi HD44780U LCD Controller

12. I/O Address Decoding • I/O address decoding determines the logical location of the I/O device • Isolated I/O • Memory-mapped I/O • Input vs. output ports • Same address does not guarantee same function! • Exhaustive address decoding • Partial address decoding

13. I/O Address Decoding (cont.) • Linear selection decoding • A single address line is used as the selection criteria for each device • Can have n input/output devices in a system with an n-bit address bus • Hazards and opportunities • Note that this idea has a very limited application space!

14. Conditional I/O • Conditional vs. unconditional transfers • I/O synchronization • Hardware example • Polling • Overhead • Flags / semaphores • Wait loops • Timeouts • Software exercise

15. ADuC7026 GPIO Ports • The ADuC7026 has 40 pins organized as 5 ports that can be used as digital GPIO • All pins have multiple functions in addition being able to be used as GPIO • The configuration selection is set through the GPxCON MMR.

16. ADuC7026 GPIO MMRs • GPxCON • Determine which of a pin’s functions are active • This is the configuration column selection on the previous slide aduc7026.inc

17. ADuC7026 GPIO MMRs (cont) • GPxPAR • PARameters • Controls whether or not the internal pull-ups are used. • Does not apply to ports 2 and 4

18. ADuC7026 GPIO MMRs (cont) • GPxDAT • Control the pin direction • Set the output state • Read the pin value • Read the pin values that were present at reset

19. ADuC7026 GPIO MMRs (cont) • GPxSET • Write 1s to set the output value • 0s have no effect

20. ADuC7026 GPIO MMRs (cont) • GPxCLR • Write 1s to clear the output value • 0s have no effect

21. General Purpose I/O Exercise • Write a program that • Configures port P1 as a GP input port and P2 as a GP output port. • Sets P2 to 0xF7 • Reads the value on P1 at reset • Copies the value on P1 to P2 • Changes the least significant nibble of P2 to C, without changing the more significant nibble

22. Wrapping Up • Reading for week8 • ADUC 53-60, 71-73, 75-79

23. ADuC7026 Clock Generation

24. ADuC7026 PLLCON

25. ADuC7026 Operating Modes

26. ADuC7026 POWCON

27. ADuC7026 Functional Block Diagram

28. MAX807

29. 74HC540/541

30. 74HC573

31. 74HC574

32. AD7865

33. Generic Device Controller

34. HitachiHD44780ULCDController

35. Conditional I/O Exercise Write a subroutine to read data from an input device like the hardware example. Assume that the flag is a READY signal (active high). If the device does not become ready after 1 trillion polling attempts, return with R0 = -1, otherwise, return with the data in R0.

36. Conditional I/O Example /MS0 base address = 0x1000 0000

37. aduc7026.inc ;GPIO GPIO_MMR_BASE EQU 0xFFFFF400 GP0CON EQU 0x00 GP1CON EQU 0x04 GP2CON EQU 0x08 GP3CON EQU 0x0C GP4CON EQU 0x10 GP0DAT EQU 0x20 GP0SET EQU 0x24 GP0CLR EQU 0x28 GP0PAR EQU 0x2C