SENIOR DESIGN 10/3

TERMINOLOGY Microcontroller vs. Microprocessor vs. Microcomputer A microprocessor is a central processing unit on a single chip. A microprocessor combined with support circuitry , peripheral I/O components and memory (RAM & ROM) used to be called a “microcomputer.” A microprocessor where all the components mentioned above are combined on the same single chip that the microprocessor is on, is called a microcontroller. We will be using the ATMEGA 8 microcontroller.

MICROCONTROLLER ARCHITECTURE

MICRCONTROLLER ARCHITECTURE 1: CPU -- fetches the instructions stored in the program memory, decodes them, and executes them. The CPU itself is composed of registers the arithmetic logic unit, the instruction decoder and control circuitry. 2: PROGRAM MEMORY: The program memory stores the instructions that form the program. To accommodate larger programs, the program memory may be partitioned as internal program memory and external program memory (in some controllers). Program memory is usually nonvolatile and is of EEPROM, EPROM, Flash, or OTP (one-time programmable) type. [EEPROM for Atmega8]. 3: RAM: The RAM is the data memory of the controller. The CPU uses RAM to store variables as well as the stack. The stack is used by the CPU to store return addresses from where to resume execution after it has completed a subroutine or an interrupt call.

MICRCONTROLLER ARCHITECTURE 4: CLOCK OSCILLATOR: The controller executes the program out of the program memory at a certain rate. This rate is determined by the frequency of the clock oscillator. The clock oscillator could be an internal RC-oscillator [this is the case for the Atmega 8], or an oscillator with an external timing element, such as a quartz crystal or RC circuit. As soon as power is applied to the controller, the oscillator starts operating. 5: RESET AND BROWNOUT DETECTOR CIRCUIT: The reset circuit in the controller ensures that at startup all the components and control circuits in the controller start at a predefined initial state and all the required registers are initialized properly. The brownout detector is a circuit that monitors the power supply voltage, and if there is a momentary drop in voltage, resets the processor so that the drop in voltage does not corrupt register and memory contents, which could lead to faulty operations.

MICRCONTROLLER ARCHITECTURE 6: SERIAL PORT: The serial port can operate at any required data transfer speed. The serial port takes data bytes from the controller and shifts out the data one bit at a time to the output. Similarly, it accepts external data a bit at a time, makes a byte out of 8 such bits, and presents this to the controller. 7: DIGITAL I/O PORT: The microcontroller uses the digital I/O components to exchange digital data with the outside world. Compared to the serial port, which transfers data a bit at a time, the data from the I/O port is exchanged as bytes. 8: ANALOG I/O PORT: Analog input is performed using an analog-to-digital converter (ADC). The controller could be equipped with an integrated ADC or an analog comparator [the Atmega 8 has both (?)] , which is used under software control to perform A-to-D conversion. ADC’s are used to acquire senor data from devices such as temperature sensors and photocells. Such sensors often produce proportional analog voltage data. Analog output is performed using a digital-to-analog converter (DAC) [must be externally in case of Atmega 8]. Most controllers are equipped with pulse-width modulators that can be used to get analog voltage with a suitable external RC filter [this is the case for the Atmega8]. DAC’s are used to drive motors, to generate sound, for visual displays.. (dimming LED’s). [SENSORS assignment].

MICRCONTROLLER ARCHITECTURE 9: TIMER: The timer is used by the controller to time events. The timer can also be used as a counter. 10: WATCHDOG TIMER: A watchdog timer (WDT) is a special timer with a specific function. It is usually used to prevent software crashes. It works as follows: Once armed, the WDT increments an internal counter at some rate. If the user program does not reset the counter, the counter overflows, which is used to reset the controller. .. . The assumption is that if the user program does not reset the WDT, it has failed in some way and therefore rather than system crash or unpredictable system performance, it is better to reset the system. 11: RTC: A real time clock (RTC) is a special timer with the task of maintaining time of day, date etc.. . It can be used to time-stamp events [must be externally added to Atmega8]. ------------------------------------------------- Like microprocessors, microcontrollers are classified as 8-bit, 16-bit, etc.. . This refers to the width of the internal registers and the accumulator. An 8-bit system usually also means that the CPU connects to the various chip component through an 8-bit data path.

MICRCONTROLLER ARCHITECTURE

FROM ATMEGA8 Datasheet. In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with separate memories and buses for program and data. Instructions in the Program memory are executed with a single level pipelining. While one instruction is being executed, the next instruction is pre-fetched from the Program memory. This concept enables instructions to be executed in every clock cycle. The Program memory is In- System Reprogrammable Flash memory. The fast-access Register File contains 32 x 8-bit general purpose working registers with a single clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical ALU operation, two operands are output from the Register File, the operation is executed, and the result is stored back in the Register File – in one clock cycle.

Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data Space addressing – enabling efficient address calculations. One of the these address pointers can also be used as an address pointer for look up tables in Flash Program memory. These added function registers are the 16-bit X-, Y-, and Z-register, described later in this section. The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register operations can also be executed in the ALU. After an arithmetic operation, the Status Register is updated to reflect information about the result of the operation. The Program flow is provided by conditional and unconditional jump and call instructions, able to directly address the whole address space. Most AVR instructions have a single 16-bit word format. Every Program memory address contains a 16- or 32-bit instruction. Program Flash memory space is divided in two sections, the Boot program section and the Application program section. Both sections have dedicated Lock Bits for write and read/write protection. The SPM instruction that writes into the Application Flash memory section must reside in the Boot program section. During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack size is only limited by the total SRAM size and the usage of the SRAM. All user programs must initialize the SP in the reset routine (before subroutines or interrupts are executed). The Stack Pointer SP is read/write accessible in the I/O space. The data SRAM can easily be accessed through the five different addressing modes supported in the AVR architecture. The memory spaces in the AVR architecture are all linear and regular memory maps. A flexible interrupt module has its control registers in the I/O space with an additional global interrupt enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector position. The lower the Interrupt Vector address, the higher the priority. The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, SPI, and other I/O functions. The I/O Memory can be accessed directly, or as the Data Space locations following those of the Register File, 0x20 - 0x5F.

ATMEGA 8 FEATURES: --- LOOK AT DATASHEET ! • High-performance, Low-power AVR® 8-bit Microcontroller • Advanced RISC Architecture – 130 Powerful Instructions – Most Single-clock Cycle Execution – 32 x 8 General Purpose Working Registers – Fully Static Operation – Up to 16 MIPS Throughput at 16 MHz – On-chip 2-cycle Multiplier • Nonvolatile Program and Data Memories – 8K Bytes of In-System Self-Programmable Flash Endurance: 10,000 Write/Erase Cycles – Optional Boot Code Section with Independent Lock Bits In-System Programming by On-chip Boot Program True Read-While-Write Operation – 512 Bytes EEPROM Endurance: 100,000 Write/Erase Cycles – 1K Byte Internal SRAM – Programming Lock for Software Security • Peripheral Features – Two 8-bit Timer/Counters with Separate Prescaler, one Compare Mode – One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture Mode – Real Time Counter with Separate Oscillator – Three PWM Channels – 8-channel ADC in TQFP and MLF package Eight Channels 10-bit Accuracy – 6-channel ADC in PDIP package – Byte-oriented Two-wire Serial Interface – Programmable Serial USART – Master/Slave SPI Serial Interface – Programmable Watchdog Timer with Separate On-chip Oscillator – On-chip Analog Comparator

ATMEGA 8 FEATURES: --- LOOK AT DATASHEET ! • Special Microcontroller Features – Power-on Reset and Programmable Brown-out Detection – Internal Calibrated RC Oscillator – External and Internal Interrupt Sources – Five Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, and Standby • I/O and Packages – 23 Programmable I/O Lines – 28-lead PDIP, 32-lead TQFP, and 32-pad MLF • Operating Voltages – 2.7 - 5.5V (ATmega8L) – 4.5 - 5.5V (ATmega8) • Speed Grades – 0 - 8 MHz (ATmega8L) – 0 - 16 MHz (ATmega8) • Power Consumption at 4 Mhz, 3V, 25°C – Active: 3.6 mA – Idle Mode: 1.0 mA – Power-down Mode: 0.5 μA

ATMEGA 8 PINOUT

ATMEGA8 / ARDUINO INTEGRATION

ATMEGA8 / ARDUINO INTEGRATION

PINMAPPING

AVR LIB & ARDUINO AVR hardware specifically designed to work with C-compiler. [Pic/ Assembly-yes, AVR/ Assembly -good luck :)]

DICE This assignment introduces you to the digital IO ports on the Atmega8. You will create a dice game using 8 digital pins. The game should do the following: 1) When the game is turned on, each possible value (1-6) will be displayed on each die. 2) Whenever the button is pressed, the dice will "roll" and then display a random value, first die one, then on die two. Supplies: 14 leds, 7 each of two different colors 10 x 1k ohm resistors 1 x 47k ohm resistor 1 momentary on pushbutton switch 2 x 2n2222 switching transistors wire

This schematic indicates the connections to the ATMEL, NOT to the Arduino ports. You have to compare the schematic below to the Arduino schematic available on our resource site, in order to complete this assignment.

Senior Design Winter Quarter