Autofocus Ranging - Canon EOS 55 Service Manual

Part 2: Technical Information
2.8 Autofocus Ranging
1. When the MPU senses that SWl is on and that ranging may start, the following
sequence determines the distance to the main subject.
2. Focusing Point Determination
2.1 Communication with Lens: Through LCLK and DLC, the MPU receives the neces-
sary
lens information.
2.2BASIS Data Accumulation
a. The BASIS reference clock, BCLK, of 500KHz is output.
b. The D / A output signals (DAI, DA2) are set.
c. The BASIS logic is reset by the CLK0, CLKl, CLK2, and READ signals.
d. The order to prepare for data accumulation is sent to the BASIS by CSAFO,
CSAFl, SCLK, and MOSI signals.
e. The order for data accumulation on four lines is sent to the BASIS by the
CLK0, CLKl, CLK2, and READ signals.
f. When each lines has reach the threshold point, the BASIS switches /TINfE
from high to low.
g. The BASIS then informs the MPU through CSAF0, CSAFl that the line has fin-
ished the data accumulation.
h. The CLK0, CLKl, CLK2, and READ signals the image data for the line, A/D
convert
it
and store
it
in the RAM.
i.
Compensation data is read through the ECS, ESK, ESQ, and ESI lines and the
image date is corrected.
2.3The RAM data is read and the prediction calculations are made for each line
(image displacement) .
2.4 The prediction calculations are converted to defocus and the lens' best focus
compensation added at this point.
3. If focus is not achieved, the lens movement is read and the focus is recalculated.
4. If focus is achieved, the active focus sensor information is sent over SPLED 1,
SPLED2, and SPLED3 to light the superimposed focus point LED.
*: If the subject is dark, the AF Illuminator is used.
RSPl.2
lll:;:818
i;
18
ii:
ii,
5
~
+------+---<---+-+-----"..,-l:
0
...J
9 g
' - - - - - ~
100 9SPLED1
_ _ _ _ _ _ ____,,.1 PLED2
' - - - - - - - - - - - - - : i s
2
PLED3
RAUX1
750
TRAUX1
2SC4081
19
XLED
MPU
EFIC
2 :,:
g;
OPAMP
181< 3,91(
Fig. 2-29 Autofocus Ranging
2-37