ECE 353 Introduction to Microprocessor Systems Michael G. Morrow, P.E. Week 7

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

ADuC7026 Block Diagram

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

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

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

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

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

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

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 Example

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

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!

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

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.

ADuC7026 GPIO MMRs GPxCON Determine which of a pins functions are active This is the configuration column selection on the previous slide aduc7026.inc

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

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

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

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

Wrapping Up Homework #4 will be due on Wednesday, October 29 th Reading for next week ADUC 53-60, 71-73, 75-79

ADuC7026 Clock Generation

ADuC7026 PLLCON

ADuC7026 Operating Modes

ADuC7026 POWCON

ADuC7026 Functional Block Diagram

MAX807

74HC540/541

74HC573

74HC574

AD7865

Generic Device Controller

Hitachi HD44780U LCD Controller

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.

Conditional I/O Example /MS0 base address = 0x

aduc7026.inc ;GPIO GPIO_MMR_BASEEQU 0xFFFFF400 GP0CONEQU0x00 GP1CONEQU0x04 GP2CONEQU0x08 GP3CONEQU0x0C GP4CONEQU0x10 GP0DATEQU0x20 GP0SETEQU0x24 GP0CLREQU0x28 GP0PAREQU0x2C