NT68P61A Datasheet, PDF (26/48 Pages) List of Unclassifed Manufacturers – 8-Bit Microcontroller for Monitor (24K OTP ROM Type)

13. H/V Sync Signals Processor
The functions of the sync processor include polarity
detection, Hsync & Vsync signals counting,
programmable sync signals output, free running signal
generator and composite sync separation. The processor
properly handles either composite or separate sync
signal inputs as well as no sync signal input. The input at
HSYNCI can be either a pure horizontal sync signal or a
composite sync signal. For the sync waveform refer to
Figures 12 and 13.
The sync processor block diagram is shown in
Figure 17. Both VSYNCI & HSYNCI pins have a Schmitt
Trigger and filtering process to improve noise immunity.
Any pulse that is shorter than 125ns will be regarded as
a glitch and will be ignored.
13.1. V & H Counter Register: VCNTL/H, HCNTL/H
Vsync counter: VCNTL/H, the 12-bit read only register,
contains information of the Vsync frequency. An internal
counter counts the numbers of 8µs pulse between two
Vsync pulses. When the next Vsync signal is recognized,
the counter is stopped and the VCNT register latches the
counter value. The counted data can be converted to the
time duration between two successive Vsync pulses by
8µs. If no Vsync comes, the counter will overflow and set
NT68P61A
VCNTOV bit (in HVCON register) to HIGH (see Figure
14). Once the VCNTOV sets to HIGH, it keeps in HIGH
state unless cleared by CLRVOV bit (in CLRFLG
register) to HIGH. When user clears the CLRVOV bit, the
VCNT counter will be reset to zero and begin to count
again.
Hsync counter: HCNTL/H, the other 12-bit read only
register pairs contain the numbers of Hsync pulse
between two Vsync pulses (see Figure 15), and the data
can be read to determine if the frequency is valid and to
determine the VIDEO mode. If the HSEL bit sets to
HIGH, the internal counter counts the Hsync pulses
between two Vsync pulses. If the HSEL bit clears to
LOW, the internal counter will be reset and begin
counting the Hsync pulses in each 8.192ms interval (see
Figure 16). The counted value will be latched by the
HCNTL/H register pairs which are updated by every
Vsync pulse or 8.192ms interval. If the counter
overflows, the HCNTOV bit (in HVCON register) will be
set to HIGH. Once the HCNTOV sets to HIGH, it remains
in the overflow HIGH state unless cleared by CLRHOV
(in CLRFLG register) to HIGH. When user clears the
CLRHOV bit, the HCNT counter will be reset to zero.
(a) Positive polarity
(b) Negative polarity
Figure 12. Separate H Sync. Waveform
(a) Positive Polarity
(b) Negative Polarity
Figure 13. Composite H Sync. Waveform
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