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Issue #213 April 2008

Programmable Power
Build a Simple USB DAC
by Yoshiyasu Takefuji

Start | USB Communications | Firmware | MAX517 (DAC) Programming | Firmware, Software, & LIBUSB | Host Device Driver Installation | Testing | Sources & PDF

Listing 3—This is a full source listing of a USB device firmware program for an ATtiny45 and a MAX517.

/* Programmable USB power supply using TINY45 and MAX517 */
#include 
#include 
#include 
#include 
#include "usbdrv.h"

void delay(unsigned int p)
{ unsigned char i, j;		//one loop is 3.8us with 12MHz
 	for(i=0;i<p;i++)  for(j=0;j<10;j++);	}

void pulse(unsigned char data)
{ if((data & 0x01)==0){PORTB = 0x00; }	//SDA=0
	else {PORTB = 0x02;  }	//SDA=1
delay(1); 	PORTB = PORTB | 0x20;	//SCL=1
delay(1);	PORTB = PORTB & 0x02; 	//SCL=0
delay(1); 	}

void start_strm()
{	          PORTB = 0x20; 		//SDA=0
	delay(1);  PORTB= 0x00; delay(1); 	}

void stop_strm()
{ PORTB = 0x20; 			//SCL=1
	delay(1);	PORTB = 0x22; 		//SDA=1
	delay(1);	}

void ack_strm()
{ PORTB = 0x00; 			//SDA=0
	delay(1);	PORTB = 0x20; 		//SCL=1
	delay(1);	PORTB = 0x00; 		//SCL=0
	delay(1);	}

/*-------------generate pulse stream---------------*/
void pulse_strm(unsigned char sda)
{ 	unsigned char i,ret;
  	for(i=0;i<8;i++){ret=(sda>>(7-i)); pulse(ret); }     }   

uchar usbFunctionSetup(uchar data[3])
{ static uchar replybuf[1];		
usbMsgPtr = replybuf;
   	if(data[1] == 0){
	   replybuf[0]=55;
	   start_strm(); pulse_strm(0x5E);	//01011110 AD1=AD0=1
	   ack_strm();  pulse_strm(0x00);	//00000000 RST=PD=A0=0
	   ack_strm(); pulse_strm(data[2]);	// data[2] is for voltage
	   ack_strm();   stop_strm(); }
  	else if(data[1] == 1){
	   replybuf[0]=11;}
  	else if(data[1] == 2) {
	   replybuf[0]=22;}	
	   return 1;	}

int main(void)
{ DDRB = 0x22;	      		// 0010 0010 PB1=SDA and PB5=SCL 
				// are output
	PORTB = 0x22;		//SDA=SCL=1
 	usbInit();
 	sei();
 	for(;;){	usbPoll();	}
 	return 0;	}
/************************end of program**************************/

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