Canon A-1 Repair Manual page 121

3. I BUS (13 P)
2V
.J.
.
,
H
c-
Th is 1s t he information output from the Input IC to
the CPU. It contains brightness (BV), low voltage
interlock (LV) and mode information CAE, BCR, EF-l,
EF-2, EF-M) and display COrSP) information . I 8US
stands fo r Input Busllne whi c h 1s the time sharing
input bus to the CPU. The busllne carries information
1n two words (one word
=
8 bits). Word 1 1s brightness
code and Word 2 is mode information.
T ·B(O)
T ·B(I)
DV (V;) BV(Yo )
EF · M
.............
AE
BC K
EF - I
EF - 2
~
: .1.
U
Fig. 3-3
T ·B(2) T ·B(')
T ·B
(e)
T ·B (')
T ·B (. ) T ·B(1)
BV On
BV (
I )
BV
(2 ) BV ( ' )
BV ( 8 )
B V( 16)
MODE
I.
MODE
2-
DISP
LV
AOCE
00
MODE I
MODE 2
0 0
0
I
I
0
I
I
Fig. 3-2
>5(
~
.)o,j
.
l.o-l.2(
V)
O-O.I(
V)
(Use Bus Checker)
Wave form:
(BUS Checker Trigger)
Fig. 3-3 and Fig. 3-4 are
I Bus samples. Word 1
(BV)
is
identical in
eachsample but Word 2 shows
AE mode 1n Fig. 3-3 and
BeK (battery check) mode
in Fig. 3-4.
T.B( 2)
T.B(3)
Hodel
1
!lodel
2
Fig. 3-3 0
0
-AE Mode
Fig. 3-4
0 1 -BCK Hade
55