a tutorial on robotics part iv

7/29/2019 A Tutorial on Robotics Part IV

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Copyright Robotix Team, IIT Kharagpur

February 3rd-5th, 2006


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A Tutorial on Robotics

Part IV : Microcontrollers & ComputerControl


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AVR Family of Microcontrollers

8-bit RISC Architecture, single cycleinstructions

Principle features include

Internal oscillators, timers, UART, SPI, PWMgeneration, ADC, analog comparator andmore

Amenability to C programming

In-System-Programmable (ISP) FlashMemory

http://www.atmel.com/products/AVR/


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ATmega8 AVR Family Member

Up to 16 MIPS throughput

8KB ISP Flash Memory, 1KB SRAM,

512Byte EEPROM 8bit / 16bit timers / counters

Three PWM channels

8 Channel 10 bit ADC, AnalogComparator

Programmable UART, SPI, TWI


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ATmega8 PDIP Package


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ATmega8 TQFP Package


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ISP Flash Memory

ISP : In-System-Programmable FlashROM

No need of specialized programmerhardware

No need to remove processor fromcircuit for reprogramming


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STK200 ISP Dongle

PonyProg Programming Softwarehttp://www.lancos.com/prog.html


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WinAVR

WinAVR is a open source softwaredevelopment suite for Atmel AVRseries of RISC microcontrollers

GUI Integrated DevelopmentEnvironment

Includes the GNU GCC compiler for C

and C++.

http://winavr.sourceforge.net/


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WinAVR IDE Screenshot


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Procyon AVRlib

AVRlib is a library of easy-to-use Cfunctions for AVR controllers

AVRlib aims to allow programmers towork quickly towards their end goalby reducing the time needed to writebasic support functions and code

http://www.procyonengineering.com/avr/avrlib/


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PWM DC Motor Control

//Dual 8-bit PWM mode setup of timer 1

timer1PWMInit (8);

// Frequency Prescaling to F_CPU_CLOCK / 256

timer1SetPrescaler (4);

// Left and right motor speed settimer1PWMASet (lSpeed); // Pin 15 (OC1A)

timer1PWMBSet (rSpeed); // Pin 16 (OC1B)

// Start on the PWM generation

timer1PWMAOn ();

timer1PWMBOn ();


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ADCs & Analog Comparator

DDRA = 0x00; // Configure Port A (ADC) as Input

PORTA = 0x00;// Disable internal pull up resistors

// Initialize Analog to Digital Converter

a2dInit();

// Set conversion speed

a2dSetPrescaler(ADC_PRESCALE_DIV32);

// Set analog voltage reference

a2dSetReference(ADC_REFERENCE_AVCC);

// Acquire analog data into digital formatfor (i = 0; i < 8; i ++)

adcData [i] = a2dConvert8bit(i);


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UART - Serial Communication

// Initialize UART at 2400 bps

uartInit();

uartSetBaudRate (2400);

// Check is data received

if (!uartReceiveBufferIsEmpty ()){

// if data received then get it in a variable

uartReceiveByte (&dataIn);

// do whatever u wish with dataIn

}


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Crystal Oscillator Clock Source


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AVR Fuse settings

CKOPT CKSEL3:0 Frequency(MHz)

C1 & C2

1 1010 0.4 0.9 -

1 1101 0.9 3.0 12 22 pf

1 1111 3.0 8.0 12 22 pf

0 1011, 1101,1111

>= 1.0 12 22 pf

SUT 1:0 = 11


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Computer Control

Parallel & Serial Port Communication


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PC Parallel Port - Features

Commonly known as the printer port

25 pin D-Type connector

It has 12 digital output pins, 5 digitalinput pins

Pins operate at the TTL voltage leveli.e. 0 5V

Port identified by a base address inthe computer I/O memory space


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PC Parallel Port Pin Layout


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PC Parallel Port I/O Registers

Most PCs have 378 Hex base address

8 output pins are accessed via the

DATA port (Base address) 4 output pins are accessed via the

CONTROL port (Base address + 2)

5 input pins are accessed via theSTATUS port (Base address + 1)


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PC Parallel Port I/O Registers

- marked bits in register byte are unused


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Accessing Parallel Port VC ++

#include

#define Data 0x378 // Base address#define Status 0x379 // Base address + 1

#define Control 0x37a // Base address + 2

int main () {unsigned char Bits;Bits = 0b11001010;

_outp(Data, Bits); /* output data */Bits = _inp(Status);/* input data */return (0);}


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PC Serial Port - Features

Most commonly 9 pin D-Typeconnector. 25 pin D-Type is rare

Pins operate at -25 to + 25 voltagelevels

Data transmitted as a bit sequence

Known as the EIA RS232C port orsimply RS232


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EIA RS232C Specifications

Logic 0 is between +3 to +25 volts

Logic 1 is between -3 to -25 volts

-3 to +3 volts region is undefined Maximum data rate of 19,600 bps


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Serial Port vs. Parallel Port

Serial cables can be much longer thatParallel cables 50V swing compared to 5V swing

Null Modem Configuration just needs3 core cable compared to 19 coreparallel port cable

Serial suited for wireless transmission Microcontrollers just need two pins

(RXD & TXD) for communication


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Null Modem Configuration

Pin 3 Transmit Data

Pin 2 Receive Data

Pin 5 Signal Ground Pin 4, 6, 1 shorted together

Pin 7, 8 shorted together


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RS-232 Waveforms

Asynchronous Communication i.e. separateclock at both ends

Frame synchronization done by the start /stop bit

Line is kept logic 1 when idle. Start bit islogic 0

Bit order from LSB to MSB


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RS-232 Level Converters

For using theRS232 data, digitaldevices need

TTL/CMOS voltagelevels

Level conversion isdone using IC

MAX232 / DS232


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RS-232 frame decoding

The decoding of the bit sequenceframe is done by computer hardware

When communicating with robots,decoding done by onboardmicrocontroller

Microcontroller Serial communication

interface is known as UART (UniversalAsynchronous Receiver Transmitter)


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Accessing Serial Port - VB

MSComm Control 6.0 is used forserial port communication


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MSComm Control Properties


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Com Port identification number

Settings: Baud Rate, Parity Check,Data Bits, Stop Bits

Hand Shaking Method : Xon/Xoff fornull-modem configuration


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InBufferSize : Input buffer size

OutBufferSize : Output buffer size

RThreshhold : Receive size forinterrupt generation

SThreshhold : Min. transmit size

InputLen : Number of bytes to bepicked up from the input buffer

EOFEnable : Search for EOF character


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ParityReplace : Parity Errorreplacement character

NullDiscard : Null characters sent tothe receive buffer or not

RTSEnable : Request to Send enable

DTREnable : Data Terminal Ready


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Example Code

Receive Data

Private Sub CommunicationTerminal_OnComm()

Dim InputBuffer As String

If CommunicationTerminal.CommEvent = comEvReceive Then

InputBuffer = CommunicationTerminal.Input

End If

Use InputBuffer as per requirement

End Sub

Transmit Data

If CommunicationTerminal.PortOpen = True ThenCommunicationTerminal.Output = Hello

End If


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Thank You

End of presentation

a tutorial on robotics part iv

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