Hitachi HV-F31CL Operation Manual page 37

(3) ALC GATE
AUTO EXPOSURE signal detect area (8 x 8) can be set as desired.
-OFF-
Setting value 2800007F h
The screen overall video signal is detected for AUTO EXPOSURE control.
-ON-
Setting value 2800807F h
GATE for detecting the AUTO EXPOSURE video signal is set in lines 1-2 to 7-8. The area is not shown on
the screen.
-Manual setting-
Detect area of ALC GATE can be arranged in 8 x 8 matrix areas.
Setting value 282xyy00 h
x: line selection
0(line1) to 7(line8)
yy: column selection
Set "1" in detect area and "0" in non-detect area to generate 8 binary digits (left side: MSB, right side:
LSB). Convert the 8 binary digits to 2 hexadecimal digits.
23
variable magnification.