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/* VGA Sync Generator
* 11/11/08 - dwan : dwanafite@yahoo.fr
*
* Based on :
* - RG Matrix Example v.2 8/1/08, by BroHogan, from the Arduino Playground
* - Simplest universal VGA/PAL terminal, by Ibragimov Maxim Rafikovich, http://www.vga-avr.narod.ru/main.html
* - the very useful Timer/Counter/Prescaler Calculator, http://www.et06.dk/atmega_timers/
* - Arduino.cc Port Manipulation Tutorial
*
* This program outputs pretty accurate VGA syncronization signals. It's using a timer interrupt on timer2, so hopefully you can make other cool things in loop().
*/
// 640 * 480 @ 60Hz - FvSync = 60.3 Hz / FhSync = 31.3 kHz
// HSync : pin 7 Arduino, pin 13 VGA
// VSync : pin 6 Arduino, pin 14 VGA
// Arduino's pin 5 is HIGH when video can be sent, LOW otherwise. I use it to power a transistor. See this wonderful page : http://www.anatekcorp.com/driving.htm
// 1 NOP = 62,5 ns wasted
#define NOP asm("nop")
#define vga_field_line_count 525 // number of VGA lines
#define ISR_FREQ 0x3F // Sets the speed of the ISR - LOWER IS FASTER - 62
volatile unsigned int linecount;
void setup()
{
//Serial.begin(9600); // set up Serial library at 9600 bps
DDRB |= B00000111;
DDRD |= B11100000; // it sets pins 7, 6 and 5 as output without changing the value of pins 0 & 1, which are RX & TX
// 76543210 <- pin translation
PORTB |= B00000111;
PORTD |= B11000000; // sets pins 7 (hSync) and 6 (vSync) HIGH
// 76543210;
setISRtimer(); // setup the timer
startISR(); // start the timer to toggle shutdown
}
void loop()
{
}
///////////////////////////// ISR Timer Functions ///////////////////////////
ISR(TIMER2_COMPA_vect)
{
// Stop video
// pin 5 LOW
PORTD &= ~(1 << 5);
// Front porch
NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP;
// Count number of lines
if (++linecount == vga_field_line_count)
{
linecount = 0;
}
// can it be vsync tiem nao ?
if ((linecount == 10 )||(linecount == 11 ))
{
// hsync LOW
// vsync LOW
PORTD &= ~(1 << 7);
PORTD &= ~(1 << 6);
}
else // ,hsync only
{
// hsync LOW
// vsync HIGH
PORTD &= ~(1 << 7);
PORTD |= (1 << 6);
}
NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP;
NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP;
NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP;
NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP;
// nonetheless,
// hsync HIGH
PORTD |= (1 << 7);
NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP;
NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP;
NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP; NOP;
NOP;
// Start video if we are in a visible area
if (linecount > 45)
{
// pin 5 HIGH
PORTD |= (1 << 5);
}
}
void setISRtimer(){ // setup ISR timer controling toggleing
TCCR2A = 0x02; // WGM22=0 + WGM21=1 + WGM20=0 = Mode2 (CTC)
TCCR2B = (1 << CS01); // /8 prescaler (2MHz)
TCNT2 = 0; // clear counter
OCR2A = ISR_FREQ; // set TOP (divisor) - see #define
}
void startISR(){ // Starts the ISR
TCNT2 = 0; // clear counter (needed here also)
TIMSK2|=(1<<OCIE2A); // set interrupts=enabled (calls ISR(TIMER2_COMPA_vect)
}
void stopISR(){ // Stops the ISR
TIMSK2&=~(1<<OCIE2A); // disable interrupts
}
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