Canon A-1 Repair Manual page 40

(4) Digital Computation and Codes
Computation is carried out in the arithmetic logic
unit (ALU for short) inside a micro computer based
on the information given by the input mechanism.
All data are processed in the form of digital
numerals. This camera is unique in that all the
data p r ocessing such as data inpu t by the Gray code
and computation are done by codes. No other camera
has had such data processing and computation system .
Data is
processed by
some of them below.
a code of 28
=
256.
processed in CPU by
8 bits and we are introducing
The 8 bits enable you to make
Notice that these data are
means of natural binary code·.
••
ASA 100
ASA 400
Shutter
Shutter
Aperture
Aperture
EV value
EV
value
speed
speed
f/4
f/5 . 6
EV 10
EV 11
1 / 250
1/500
MSD LSD
00100000
00110000
10001000
10010000
00101000
00110000
10100000
10101000
Code tables in the Repair Guide are written with
the least significant digit (LSD) at the left
for ease of use with test equipment.
Based on these data, computation, in addition and
subtraction of data takes place very rapidly in CPU
through the APEX system. This helps determine
correct exposure. The APEX system computes data
through addition and subtraction with the applied
logarithm . .
The basic APEX formula is:
EV = TV
+
AV = BV
+
SV
4 1