Canon A-1 Repair Manual page 41

42
For your reference, the conventional computation
system is carried out through multiplication,
division and square.
2 EV =
A2
BS
-
T
K
Ev --- exposure value
A f-number
T
shutter speed
B
brightness of the subject
S film speed
K
constant
For a detail discussion of the APEX system, refer
to the General section of the AE-l Repair Manual.
(5) Display Information
computed results such as shutter speed, aperture and
other information required for determining exposure
are all displayed in r e d LED's through the decoder"
driver. The viewfinder information is displayed in
the dynamic display method which is helpful in
reducing the number of wires and power consumption,
and cutting cost. See the figure 13. (a) describes
the static display method, (b) shows the principles
of the dyn amic display method, and " (c) shows the
timing chart.
In the static display method, the counter output is
input into the decoder driver by means of four lines.
After being decoded for a seven-segment LED display,
signals are transmitted into the seven-segment LED
display by means of seven lines. This means that
the static display method needs the same number of
counte r s and decoders as it has display digits.
The necessary number of wires amounts to the digit
number multiplied by seven.
On the other hand, the dynamic display method
requ ires only one decoder driver through one multi-
plexer without regard to the number of digits. The
Wiring simply requires for seven lines to be
connected. As far as the display is concerned, each
digit should be provided with the ground line and
transistor switch.