M3727GM6 Datasheet, PDF (51/129 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER with CLOSED CAPTION DECODER and ON-SCREEN DISPLAY CONTROLLER

M3727GM6/M8–XXXSP/FP M37272E8SP/FP
8.10.2 Clamping Circuit and Low-pass Filter
The clamp circuit clamps the sync chip part of the composite video
signal input from the CVIN pin. The low-pass filter attenuates the noise
of clamped composite video signal. The CVIN pin to which composite
video signal is input requires a capacitor (0.1 µF) coupling outside.
Pull down the CVIN pin with a resistor of hundreds of kiloohms to 1
MΩ. In addition, we recommend to install externally a simple low-
pass filter using a resistor and a capacitor at the CVIN pin (refer to
Figure 8.10.1).
8.10.3 Sync Slice Circuit
This circuit takes out a composite sync signal from the output signal
of the low-pass filter.
8.10.4 Synchronous Signal Separation Circuit
This circuit separates a horizontal synchronous signal and a vertical
synchronous signal from the composite sync signal taken out in the
sync slice circuit.
(1)Horizontal Synchronous Signal (Hsep)
A one-shot horizontal synchronizing signal Hsep is generated at
the falling edge of the composite sync signal.
(2)Vertical Synchronous Signal (Vsep)
As a Vsep signal generating method, it is possible to select one of
the following 2 methods by using bit 4 of the data slicer control
register 2 (address 00E116).
•Method 1 The LOW level width of the composite sync signal is
measured. If this width exceeds a certain time, a Vsep
signal is generated in synchronization with the rising
of the timing signal immediately after this LOW level.
•Method 2 The LOW level width of the composite sync signal is
measured. If this width exceeds a certain time, it is
detected whether a falling of the composite sync sig-
nal exits or not in the LOW level period of the timing
signal immediately after this LOW level. If a falling
exists, a Vsep signal is generated in synchronization
with the rising of the timing signal (refer to Figure
8.10.6).
Figure 8.10.6 shows a Vsep generating timing. The timing signal shown
in the figure is generated from the reference clock which the timing
generating circuit outputs.
Reading bit 5 of data slicer control register 2 permits determinating
the shape of the V-pulse portion of the composite sync signal. As
shown in Figure 8.10.7, when the A level matches the B level, this bit
is “0.” In the case of a mismatch, the bit is “1.”
Composite s
Timing
signal
Measure LOW period
Vsep signal
A Vsep signal is generated at a rising of the timing signal
immediately after the LOW level width of the composite
sync signal exceeds a certain time.
Fig. 8.10.6 Vsep Generating Timing (method 2)
Rev.1.00 Apr 01, 2001 page 51 of 127
REJ03B0132-0100Z