Canon Camera Hackers Manual

Contents

7.6 Communications 2117.6 CommunicationsIn this section, we will discuss the camera uplink to a PC as well as serialcommunication with an external device.7.6.1 USB uploadBecause the USB port, by default, is reserved for the remote control, youmust explicitly disable the option ALT > MENU > Scripting > Disable USBDownload if you want to upload (or download, depending on your angle ofview) images onto a PC. Of course, the camera must be switched to Replaymode when uploading images.The SDM upload functions are designed to work closely together withthe WIA Loader (www.mortara.org/index.php/software/windows/49-wia-loader), a Windows (.NET) based image uploader. (On Linux and MacOS X, itcan run under the Mono-Framework 2.4.) The WIA Loader can, for example,take care of stereo image pairs from twin cameras (section 7.7.4). It canrename such images, place them in left and right folders, and rotate im-ages losslessly if one camera is mounted upside down in a Z-frame.Because transmission takes place through the USB port, the card canremain in the camera. This has advantages in that the camera doesn’t needto be removed from an elaborate set-up and that the card is never forgot-ten in the computer. The WIA loader can even automatically remove trans-mitted images from the card. Because the SDM allows uploading imagesvia script commands (section 7.9), you can (almost) simulate tetheredshooting—at least for time-lapse operation. After an image has beentaken, the interval between two pictures can be used to upload the imageto the connected PC. And because the WIA loader can also delete the imagefrom the card, it never runs out of capacity.7.6.2 Serial communicationsNot only can the SDM communicate with a PC, it also offers the possibilityof using the blue LED as an optical serial port. A light-sensitive cell glued tothis LED and connected to a microcontroller (or to the sound card of a PC) isall the hardware required for receiving data from the camera. A set of scriptcommands (section 7.9) is available to initialize the interface and to senddata to the connected external device. The device can even acknowledgethe successful reception by sending a signal to the V+ pin (supply voltage)of the camera’s USB port (ALT > MENU > Scripting > Disable USB Downloadmust be enabled). This is not absolutely necessary but leads to more reli-able communication.