Canon A-1 Repair Manual page 29

28
maximum aperture correction for lenses brighter than
f/2.8, self-timer setting, and the use of stopped-down
metering lever , registers with a digital switch. Only
light metering is in the analog form and analog-to-
digital converter is used to generate digital signals.
The micro-computer receives all digital information
while signals which come out from the analog-to-
digital converter are loaded to the micro-computer
after gOing through the input bus line. Then the
micro-computer perform arithmetic operations on the
signals. In the A-I, the micro-qomputer first stores
the exposure value (EV) and then does the arithmetic
operation. The merit of the new system is that with
the A-I, the exposure value (EV) is stored by pressing
the exposure memory button so the camera user is at
liberty to change the combination of ABA film speed
setting, shutter speed and aperture opening.
The result of the computed value is decoded by the
decoder driver after going through the output busline,
before the exposure information appears in the view-
finder in the form of seven-segmented glowing red LED
display. On the other hand, the program storage
contains the instructi ons for the operational sequence
and performs the function of procedure and control 'of
the exposure mode selector such as shutter speed
priority AE, aperture priority AE, and programmed AE.
The existence of the program unit with the program-
mable logic array makes possible the input of infor-
mation in the fashion of a single-lever-and-dial move-
ment. The capability o f this
data~loading
program is
evidenced by the placement of the entirely innovative
AE mode selector and AT dial stop the camera.
As you press the shutter-release button, the magnetic
release is activated and while the automatic aperture
control of the FD lens activates, automatic exposure
mechanism coupled to the l e ns aperture signal pin
commences to function and then the precious metal wire
brush wipes over the segmented aperture value electrode
(SAVE) plate at
h~gh
speed. Automatic exposure aper-
ture setting is determined when the countdown of pulses
and the f/stop control functions generated by the CPU
coincide. While the pro?er f/stop value is taken
care of, shutter control activated ' by the digital
switch accurately converts the signals to specific
shutter speeds in a digital way by a reading made
within the computer. Thus after a duration of a
deSignated time following the travel of the first
curtain, the CPU sends a signal to the Magnet 3 to
close the second curtain.