Canon T90 - Power Features

Power Features

The T90 includes an integral motor driven film advance, focal plane shutter, mirror and aperture cocking and rewind functions. Canon broke new ground with the powered features of the camera. Previously, cameras used one powerful electric motor geared to all functions. Instead, the T90 has three coreless micromotors within the body, close to the functions they drove, for maximum mechanical advantage. One was used to wind the film, achieving a high-speed rate of 4.5 frames per second. A second prepared the shutter, mirror etc. for the next shot. A third motor powered the rewind function. All of this is driven by four AA batteries in the base of the camera.

To control the camera's systems, the T90 uses a dual CPU architecture. The main, low-power CPU runs at 32 kHz while the sub-CPU runs at 1 MHz, and is powered down when not needed. The main CPU handles the LCD display and overall state, while the sub-CPU handles exposure calculations, viewfinder display, and control of the camera's motors. This architecture provides for lower power usage. Both CPUs, plus other integrated circuits and components, are mounted on several flexible circuit boards that fit around the camera's structure.

A coin-type lithium battery on the main circuit board retains camera settings when the AA batteries are removed. This is not a user-serviceable part, and when it fails the camera has to be brought to a service center where the battery can be replaced by a Canon technician. Expected battery life is on the order of five years, although this depended on a variety of factors including how the duration of periods without main battery (4xAA) power.