Sebastian Barrera
/
ov7670
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ov7670.cpp
- Committer:
- edodm85
- Date:
- 2014-04-05
- Revision:
- 4:119b4c04a4ed
- Parent:
- 3:b40a945dd672
File content as of revision 4:119b4c04a4ed:
#include "ov7670.h"
OV7670::OV7670(PinName sda, PinName scl, PinName vs, PinName hr, PinName we, PortName port, int mask, PinName rt, PinName o, PinName rc) : _i2c(sda,scl),vsync(vs),href(hr),wen(we),data(port,mask),rrst(rt),oe(o),rclk(rc)
{
_i2c.stop();
_i2c.frequency(OV7670_I2CFREQ);
vsync.fall(this,&OV7670::VsyncHandler); // interrupt fall edge
CaptureReq = false;
Busy = false;
Done = false;
LineCounter = 0;
rrst = 1;
oe = 1;
rclk = 1;
wen = 0;
}
OV7670::~OV7670()
{
}
// capture request
void OV7670::CaptureNext(void)
{
CaptureReq = true;
Busy = true;
}
// capture done? (with clear)
bool OV7670::CaptureDone(void)
{
bool result;
if (Busy)
{
result = false;
}else
{
result = Done;
Done = false;
}
return result;
}
// vsync handler
void OV7670::VsyncHandler(void)
{
// Capture Enable
if (CaptureReq)
{
wen = 1;
Done = false;
CaptureReq = false;
}else
{
wen = 0;
if (Busy)
{
Busy = false;
Done = true;
}
}
}
// Data Read
int OV7670::ReadOnebyte(void)
{
int B1;
rclk = 1;
B1 = (((data&0x07800000)>>19)|((data&0x078000)>>15));
rclk = 0;
return B1;
}
// Data Start read from FIFO
void OV7670::ReadStart(void)
{
rrst = 0;
oe = 0;
wait_us(1);
rclk = 0;
wait_us(1);
rclk = 1;
wait_us(1);
rrst = 1;
}
// Data Stop read from FIFO
void OV7670::ReadStop(void)
{
oe = 1;
ReadOnebyte();
rclk = 1;
}
void OV7670::Reset(void)
{
WriteReg(0x12, 0x80); // RESET CAMERA
wait_ms(200);
}
int OV7670::Init(char c, int n)
{
if(c == 'b' || c == 'y') // YUV
{
format_temp = "BAW";
}
else
if(c == 'r') // RGB565
{
format_temp = "RGB";
}
return Init(format_temp, n);
}
int OV7670::Init(char *format, int n)
{
if (ReadReg(REG_PID) != 0x76) // check id camera
{
return 0;
}
Reset(); // Resets all registers to default values
Reset(); // Resets all registers to default values
WriteReg(REG_RGB444, 0x00); // Disable RGB444
WriteReg(REG_COM10, 0x02); // 0x02 VSYNC negative (http://nasulica.homelinux.org/?p=959)
WriteReg(REG_MVFP, 0x27); // mirror image
WriteReg(REG_CLKRC, 0x80); // prescaler x1
WriteReg(DBLV, 0x0a); // bypass PLL
WriteReg(REG_COM11, 0x0A) ;
WriteReg(REG_TSLB, 0x04); // 0D = UYVY 04 = YUYV
WriteReg(REG_COM13, 0x88); // connect to REG_TSLB
if((strcmp("BAW", format) == 0) || (strcmp("YUV", format) == 0)|| (strcmp("RAW", format) == 0)) // YUV
{
WriteReg(REG_COM7, 0x00); // YUV
WriteReg(REG_COM17, 0x00); // color bar disable
WriteReg(REG_COM3, 0x04);
WriteReg(REG_COM15, 0xC0); // Set normal rgb with Full range
}else
if((strcmp("RGB", format) == 0)) // RGB565
{
WriteReg(REG_COM7, 0x04); // RGB + color bar disable
WriteReg(REG_RGB444, 0x00); // Disable RGB444
WriteReg(REG_COM15, 0x10); // Set rgb565 with Full range 0xD0
WriteReg(REG_COM3, 0x04);
WriteReg(REG_CLKRC, 0x80); // prescaler x1
}
WriteReg(0x70, 0x3A); // Scaling Xsc
WriteReg(0x71, 0x35); // Scaling Ysc
WriteReg(0xA2, 0x02); // pixel clock delay
if(n == 19200) // 160*120
{
WriteReg(REG_COM14, 0x1a); // divide by 4
WriteReg(0x72, 0x22); // downsample by 4
WriteReg(0x73, 0xf2); // divide by 4
WriteReg(REG_HREF, 0xa4);
WriteReg(REG_HSTART, 0x16);
WriteReg(REG_HSTOP, 0x04);
WriteReg(REG_VREF, 0x0a);
WriteReg(REG_VSTART, 0x02);
WriteReg(REG_VSTOP, 0x7a);
WriteReg(0x7a, 0x20);
WriteReg(0x7b, 0x1c);
WriteReg(0x7c, 0x28);
WriteReg(0x7d, 0x3c);
WriteReg(0x7e, 0x5a);
WriteReg(0x7f, 0x68);
WriteReg(0x80, 0x76);
WriteReg(0x81, 0x80);
WriteReg(0x82, 0x88);
WriteReg(0x83, 0x8f);
WriteReg(0x84, 0x96);
WriteReg(0x85, 0xa3);
WriteReg(0x86, 0xaf);
WriteReg(0x87, 0xc4);
WriteReg(0x88, 0xd7);
WriteReg(0x89, 0xe8);
WriteReg(0x13, 0xe0);
WriteReg(0x00, 0x00);
WriteReg(0x10, 0x00);
WriteReg(0x0d, 0x40);
WriteReg(0x14, 0x18);
WriteReg(0xa5, 0x05);
WriteReg(0xab, 0x07);
WriteReg(0x24, 0x95);
WriteReg(0x25, 0x33);
WriteReg(0x26, 0xe3);
WriteReg(0x9f, 0x78);
WriteReg(0xa0, 0x68);
WriteReg(0xa1, 0x03);
WriteReg(0xa6, 0xd8);
WriteReg(0xa7, 0xd8);
WriteReg(0xa8, 0xf0);
WriteReg(0xa9, 0x90);
WriteReg(0xaa, 0x94);
WriteReg(0x13, 0xe5);
WriteReg(0x0e, 0x61);
WriteReg(0x0f, 0x4b);
WriteReg(0x16, 0x02);
WriteReg(0x21, 0x02);
WriteReg(0x22, 0x91);
WriteReg(0x29, 0x07);
WriteReg(0x33, 0x0b);
WriteReg(0x35, 0x0b);
WriteReg(0x37, 0x1d);
WriteReg(0x38, 0x71);
WriteReg(0x39, 0x2a);
WriteReg(0x3c, 0x78);
WriteReg(0x4d, 0x40);
WriteReg(0x4e, 0x20);
WriteReg(0x69, 0x00);
WriteReg(0x74, 0x10);
WriteReg(0x8d, 0x4f);
WriteReg(0x8e, 0x00);
WriteReg(0x8f, 0x00);
WriteReg(0x90, 0x00);
WriteReg(0x91, 0x00);
WriteReg(0x92, 0x00);
WriteReg(0x96, 0x00);
WriteReg(0x9a, 0x80);
WriteReg(0xb0, 0x84);
WriteReg(0xb1, 0x0c);
WriteReg(0xb2, 0x0e);
WriteReg(0xb3, 0x82);
WriteReg(0xb8, 0x0a);
WriteReg(0x43, 0x0a);
WriteReg(0x44, 0xf0);
WriteReg(0x45, 0x34);
WriteReg(0x46, 0x58);
WriteReg(0x47, 0x28);
WriteReg(0x48, 0x3a);
WriteReg(0x59, 0x88);
WriteReg(0x5a, 0x88);
WriteReg(0x5b, 0x44);
WriteReg(0x5c, 0x67);
WriteReg(0x5d, 0x49);
WriteReg(0x5e, 0x0e);
WriteReg(0x64, 0x04);
WriteReg(0x65, 0x20);
WriteReg(0x66, 0x05);
WriteReg(0x94, 0x04);
WriteReg(0x95, 0x08);
WriteReg(0x6c, 0x0a);
WriteReg(0x6d, 0x55);
WriteReg(0x6e, 0x11);
WriteReg(0x6f, 0x9f);
WriteReg(0x6a, 0x40);
WriteReg(0x01, 0x40);
WriteReg(0x02, 0x40);
WriteReg(0x13, 0xe7);
WriteReg(0x15, 0x02);
WriteReg(0x4f, 0x80);
WriteReg(0x50, 0x80);
WriteReg(0x51, 0x00);
WriteReg(0x52, 0x22);
WriteReg(0x53, 0x5e);
WriteReg(0x54, 0x80);
WriteReg(0x58, 0x9e);
WriteReg(0x41, 0x08);
WriteReg(0x3f, 0x00);
WriteReg(0x75, 0x05);
WriteReg(0x76, 0xe1);
WriteReg(0x4c, 0x00);
WriteReg(0x77, 0x01);
WriteReg(0x3d, 0xc1);
WriteReg(0x4b, 0x09);
WriteReg(0xc9, 0x60);
WriteReg(0x41, 0x38);
WriteReg(0x56, 0x40);
WriteReg(0x34, 0x11);
WriteReg(0x3b, 0x02);
WriteReg(0xa4, 0x88);
WriteReg(0x96, 0x00);
WriteReg(0x97, 0x30);
WriteReg(0x98, 0x20);
WriteReg(0x99, 0x30);
WriteReg(0x9a, 0x84);
WriteReg(0x9b, 0x29);
WriteReg(0x9c, 0x03);
WriteReg(0x9d, 0x4c);
WriteReg(0x9e, 0x3f);
WriteReg(0x78, 0x04);
WriteReg(0x79, 0x01);
WriteReg(0xc8, 0xf0);
WriteReg(0x79, 0x0f);
WriteReg(0xc8, 0x00);
WriteReg(0x79, 0x10);
WriteReg(0xc8, 0x7e);
WriteReg(0x79, 0x0a);
WriteReg(0xc8, 0x80);
WriteReg(0x79, 0x0b);
WriteReg(0xc8, 0x01);
WriteReg(0x79, 0x0c);
WriteReg(0xc8, 0x0f);
WriteReg(0x79, 0x0d);
WriteReg(0xc8, 0x20);
WriteReg(0x79, 0x09);
WriteReg(0xc8, 0x80);
WriteReg(0x79, 0x02);
WriteReg(0xc8, 0xc0);
WriteReg(0x79, 0x03);
WriteReg(0xc8, 0x40);
WriteReg(0x79, 0x05);
WriteReg(0xc8, 0x30);
WriteReg(0x79, 0x26);
WriteReg(0x09, 0x03);
WriteReg(0x3b, 0x42);
WriteReg(0xff, 0xff); /* END MARKER */
}
if(n == 76800) // 320*240
{
WriteReg(REG_COM14, 0x19);
WriteReg(0x72, 0x11);
WriteReg(0x73, 0xf1);
WriteReg(REG_HREF, 0x24);
WriteReg(REG_HSTART, 0x16);
WriteReg(REG_HSTOP, 0x04);
WriteReg(REG_VREF, 0x0a);
WriteReg(REG_VSTART,0x02);
WriteReg(REG_VSTOP, 0x7a);
WriteReg(0x7a, 0x20);
WriteReg(0x7b, 0x1c);
WriteReg(0x7c, 0x28);
WriteReg(0x7d, 0x3c);
WriteReg(0x7e, 0x55);
WriteReg(0x7f, 0x68);
WriteReg(0x80, 0x76);
WriteReg(0x81, 0x80);
WriteReg(0x82, 0x88);
WriteReg(0x83, 0x8f);
WriteReg(0x84, 0x96);
WriteReg(0x85, 0xa3);
WriteReg(0x86, 0xaf);
WriteReg(0x87, 0xc4);
WriteReg(0x88, 0xd7);
WriteReg(0x89, 0xe8);
WriteReg(0x13, 0xe0);
WriteReg(0x00, 0x00);
WriteReg(0x10, 0x00);
WriteReg(0x0d, 0x00);
WriteReg(0x14, 0x28);
WriteReg(0xa5, 0x05);
WriteReg(0xab, 0x07);
WriteReg(0x24, 0x75);
WriteReg(0x25, 0x63);
WriteReg(0x26, 0xA5);
WriteReg(0x9f, 0x78);
WriteReg(0xa0, 0x68);
WriteReg(0xa1, 0x03);
WriteReg(0xa6, 0xdf);
WriteReg(0xa7, 0xdf);
WriteReg(0xa8, 0xf0);
WriteReg(0xa9, 0x90);
WriteReg(0xaa, 0x94);
WriteReg(0x13, 0xe5);
WriteReg(0x0e, 0x61);
WriteReg(0x0f, 0x4b);
WriteReg(0x16, 0x02);
WriteReg(0x21, 0x02);
WriteReg(0x22, 0x91);
WriteReg(0x29, 0x07);
WriteReg(0x33, 0x0b);
WriteReg(0x35, 0x0b);
WriteReg(0x37, 0x1d);
WriteReg(0x38, 0x71);
WriteReg(0x39, 0x2a);
WriteReg(0x3c, 0x78);
WriteReg(0x4d, 0x40);
WriteReg(0x4e, 0x20);
WriteReg(0x69, 0x00);
WriteReg(0x6b, 0x00);
WriteReg(0x74, 0x19);
WriteReg(0x8d, 0x4f);
WriteReg(0x8e, 0x00);
WriteReg(0x8f, 0x00);
WriteReg(0x90, 0x00);
WriteReg(0x91, 0x00);
WriteReg(0x92, 0x00);
WriteReg(0x96, 0x00);
WriteReg(0x9a, 0x80);
WriteReg(0xb0, 0x84);
WriteReg(0xb1, 0x0c);
WriteReg(0xb2, 0x0e);
WriteReg(0xb3, 0x82);
WriteReg(0xb8, 0x0a);
WriteReg(0x43, 0x14);
WriteReg(0x44, 0xf0);
WriteReg(0x45, 0x34);
WriteReg(0x46, 0x58);
WriteReg(0x47, 0x28);
WriteReg(0x48, 0x3a);
WriteReg(0x59, 0x88);
WriteReg(0x5a, 0x88);
WriteReg(0x5b, 0x44);
WriteReg(0x5c, 0x67);
WriteReg(0x5d, 0x49);
WriteReg(0x5e, 0x0e);
WriteReg(0x64, 0x04);
WriteReg(0x65, 0x20);
WriteReg(0x66, 0x05);
WriteReg(0x94, 0x04);
WriteReg(0x95, 0x08);
WriteReg(0x6c, 0x0a);
WriteReg(0x6d, 0x55);
WriteReg(0x6e, 0x11);
WriteReg(0x6f, 0x9f);
WriteReg(0x6a, 0x40);
WriteReg(0x01, 0x40);
WriteReg(0x02, 0x40);
WriteReg(0x13, 0xe7);
WriteReg(0x15, 0x02);
WriteReg(0x4f, 0x80);
WriteReg(0x50, 0x80);
WriteReg(0x51, 0x00);
WriteReg(0x52, 0x22);
WriteReg(0x53, 0x5e);
WriteReg(0x54, 0x80);
WriteReg(0x58, 0x9e);
WriteReg(0x41, 0x08);
WriteReg(0x3f, 0x00);
WriteReg(0x75, 0x05);
WriteReg(0x76, 0xe1);
WriteReg(0x4c, 0x00);
WriteReg(0x77, 0x01);
WriteReg(0x3d, 0xc2);
WriteReg(0x4b, 0x09);
WriteReg(0xc9, 0x60);
WriteReg(0x41, 0x38);
WriteReg(0x56, 0x40);
WriteReg(0x34, 0x11);
WriteReg(0x3b, 0x02);
WriteReg(0xa4, 0x89);
WriteReg(0x96, 0x00);
WriteReg(0x97, 0x30);
WriteReg(0x98, 0x20);
WriteReg(0x99, 0x30);
WriteReg(0x9a, 0x84);
WriteReg(0x9b, 0x29);
WriteReg(0x9c, 0x03);
WriteReg(0x9d, 0x4c);
WriteReg(0x9e, 0x3f);
WriteReg(0x78, 0x04);
WriteReg(0x79, 0x01);
WriteReg(0xc8, 0xf0);
WriteReg(0x79, 0x0f);
WriteReg(0xc8, 0x00);
WriteReg(0x79, 0x10);
WriteReg(0xc8, 0x7e);
WriteReg(0x79, 0x0a);
WriteReg(0xc8, 0x80);
WriteReg(0x79, 0x0b);
WriteReg(0xc8, 0x01);
WriteReg(0x79, 0x0c);
WriteReg(0xc8, 0x0f);
WriteReg(0x79, 0x0d);
WriteReg(0xc8, 0x20);
WriteReg(0x79, 0x09);
WriteReg(0xc8, 0x80);
WriteReg(0x79, 0x02);
WriteReg(0xc8, 0xc0);
WriteReg(0x79, 0x03);
WriteReg(0xc8, 0x40);
WriteReg(0x79, 0x05);
WriteReg(0xc8, 0x30);
WriteReg(0x79, 0x26);
WriteReg(0x09, 0x03);
WriteReg(0x3b, 0x42);
WriteReg(0xff, 0xff); /* END MARKER */
}
if(n == 307200) // 640*480
{
WriteReg(REG_CLKRC, 0x01);
WriteReg(REG_TSLB, 0x04);
WriteReg(REG_COM7, 0x01);
WriteReg(DBLV, 0x4a);
WriteReg(REG_COM3, 0);
WriteReg(REG_COM14, 0);
WriteReg(REG_HSTART, 0x13);
WriteReg(REG_HSTOP, 0x01);
WriteReg(REG_HREF, 0xb6);
WriteReg(REG_VSTART, 0x02);
WriteReg(REG_VSTOP, 0x7a);
WriteReg(REG_VREF, 0x0a);
WriteReg(0x72, 0x11);
WriteReg(0x73, 0xf0);
/* Gamma curve values */
WriteReg(0x7a, 0x20);
WriteReg(0x7b, 0x10);
WriteReg(0x7c, 0x1e);
WriteReg(0x7d, 0x35);
WriteReg(0x7e, 0x5a);
WriteReg(0x7f, 0x69);
WriteReg(0x80, 0x76);
WriteReg(0x81, 0x80);
WriteReg(0x82, 0x88);
WriteReg(0x83, 0x8f);
WriteReg(0x84, 0x96);
WriteReg(0x85, 0xa3);
WriteReg(0x86, 0xaf);
WriteReg(0x87, 0xc4);
WriteReg(0x88, 0xd7);
WriteReg(0x89, 0xe8);
/* AGC and AEC parameters. Note we start by disabling those features,
then turn them only after tweaking the values. */
WriteReg(0x13, COM8_FASTAEC | COM8_AECSTEP | COM8_BFILT);
WriteReg(0x00, 0);
WriteReg(0x10, 0);
WriteReg(0x0d, 0x40);
WriteReg(0x14, 0x18);
WriteReg(0xa5, 0x05);
WriteReg(0xab, 0x07);
WriteReg(0x24, 0x95);
WriteReg(0x25, 0x33);
WriteReg(0x26, 0xe3);
WriteReg(0x9f, 0x78);
WriteReg(0xa0, 0x68);
WriteReg(0xa1, 0x03);
WriteReg(0xa6, 0xd8);
WriteReg(0xa7, 0xd8);
WriteReg(0xa8, 0xf0);
WriteReg(0xa9, 0x90);
WriteReg(0xaa, 0x94);
WriteReg(0x13, COM8_FASTAEC|COM8_AECSTEP|COM8_BFILT|COM8_AGC|COM8_AEC);
/* Almost all of these are magic "reserved" values. */
WriteReg(0x0e, 0x61);
WriteReg(0x0f, 0x4b);
WriteReg(0x16, 0x02);
WriteReg(0x1e, 0x27);
WriteReg(0x21, 0x02);
WriteReg(0x22, 0x91);
WriteReg(0x29, 0x07);
WriteReg(0x33, 0x0b);
WriteReg(0x35, 0x0b);
WriteReg(0x37, 0x1d);
WriteReg(0x38, 0x71);
WriteReg(0x39, 0x2a);
WriteReg(0x3c, 0x78);
WriteReg(0x4d, 0x40);
WriteReg(0x4e, 0x20);
WriteReg(0x69, 0);
WriteReg(0x6b, 0x0a);
WriteReg(0x74, 0x10);
WriteReg(0x8d, 0x4f);
WriteReg(0x8e, 0);
WriteReg(0x8f, 0);
WriteReg(0x90, 0);
WriteReg(0x91, 0);
WriteReg(0x96, 0);
WriteReg(0x9a, 0);
WriteReg(0xb0, 0x84);
WriteReg(0xb1, 0x0c);
WriteReg(0xb2, 0x0e);
WriteReg(0xb3, 0x82);
WriteReg(0xb8, 0x0a);
/* More reserved magic, some of which tweaks white balance */
WriteReg(0x43, 0x0a);
WriteReg(0x44, 0xf0);
WriteReg(0x45, 0x34);
WriteReg(0x46, 0x58);
WriteReg(0x47, 0x28);
WriteReg(0x48, 0x3a);
WriteReg(0x59, 0x88);
WriteReg(0x5a, 0x88);
WriteReg(0x5b, 0x44);
WriteReg(0x5c, 0x67);
WriteReg(0x5d, 0x49);
WriteReg(0x5e, 0x0e);
WriteReg(0x6c, 0x0a);
WriteReg(0x6d, 0x55);
WriteReg(0x6e, 0x11);
WriteReg(0x6f, 0x9f);
WriteReg(0x6a, 0x40);
WriteReg(0x01, 0x40);
WriteReg(0x02, 0x60);
WriteReg(0x13, COM8_FASTAEC|COM8_AECSTEP|COM8_BFILT|COM8_AGC|COM8_AEC|COM8_AWB);
/* Matrix coefficients */
WriteReg(0x4f, 0x80);
WriteReg(0x50, 0x80);
WriteReg(0x51, 0);
WriteReg(0x52, 0x22);
WriteReg(0x53, 0x5e);
WriteReg(0x54, 0x80);
WriteReg(0x58, 0x9e);
WriteReg(0x41, 0x08);
WriteReg(0x3f, 0);
WriteReg(0x75, 0x05);
WriteReg(0x76, 0xe1);
WriteReg(0x4c, 0);
WriteReg(0x77, 0x01);
WriteReg(0x3d, 0xc3);
WriteReg(0x4b, 0x09);
WriteReg(0xc9, 0x60);
WriteReg(0x41, 0x38);
WriteReg(0x56, 0x40);
WriteReg(0x34, 0x11);
WriteReg(0x3b, COM11_EXP|COM11_HZAUTO);
WriteReg(0xa4, 0x88);
WriteReg(0x96, 0);
WriteReg(0x97, 0x30);
WriteReg(0x98, 0x20);
WriteReg(0x99, 0x30);
WriteReg(0x9a, 0x84);
WriteReg(0x9b, 0x29);
WriteReg(0x9c, 0x03);
WriteReg(0x9d, 0x4c);
WriteReg(0x9e, 0x3f);
WriteReg(0x78, 0x04);
/* Extra-weird stuff. Some sort of multiplexor register */
WriteReg(0x79, 0x01);
WriteReg(0xc8, 0xf0);
WriteReg(0x79, 0x0f);
WriteReg(0xc8, 0x00);
WriteReg(0x79, 0x10);
WriteReg(0xc8, 0x7e);
WriteReg(0x79, 0x0a);
WriteReg(0xc8, 0x80);
WriteReg(0x79, 0x0b);
WriteReg(0xc8, 0x01);
WriteReg(0x79, 0x0c);
WriteReg(0xc8, 0x0f);
WriteReg(0x79, 0x0d);
WriteReg(0xc8, 0x20);
WriteReg(0x79, 0x09);
WriteReg(0xc8, 0x80);
WriteReg(0x79, 0x02);
WriteReg(0xc8, 0xc0);
WriteReg(0x79, 0x03);
WriteReg(0xc8, 0x40);
WriteReg(0x79, 0x05);
WriteReg(0xc8, 0x30);
WriteReg(0x79, 0x26);
WriteReg(0xff, 0xff); /* END MARKER */
}
return 1;
}
// write to camera
void OV7670::WriteReg(int addr,int data)
{
_i2c.start();
_i2c.write(OV7670_WRITE);
wait_us(OV7670_WRITEWAIT);
_i2c.write(addr);
wait_us(OV7670_WRITEWAIT);
_i2c.write(data);
_i2c.stop();
}
// read from camera
int OV7670::ReadReg(int addr)
{
int data;
_i2c.start();
_i2c.write(OV7670_WRITE);
wait_us(OV7670_WRITEWAIT);
_i2c.write(addr);
_i2c.stop();
wait_us(OV7670_WRITEWAIT);
_i2c.start();
_i2c.write(OV7670_READ);
wait_us(OV7670_WRITEWAIT);
data = _i2c.read(OV7670_NOACK);
_i2c.stop();
return data;
}