Rev. 1.0, 02/00, page 771 of 1141
Csync
HVTH
SEPH
Digital H separation
counter
About
3.2
µ
s to 2.0
µ
s
Figure 27.4 HVTH Value and SEPH Generation Timing
When Equalizing Pulses Are Not Detected
The following shows examples of HVTHR settings.
Condition:
(HVTHR – 1)
×
(2/OSC) > 1.6
µ
s or 3.2
µ
s
System clock OSC = 10 MHz
2/OSC = 5 MHz = 0.2
µ
s
Example 1: To detect equalizing pulses
Hsync detection threshold value: 1.6
µ
s
1.6
µ
s / 0.2
µ
s = 8
HVTHR value = H'8 (8)
Example 2: To not detect equalizing pulses
Hsync detection threshold value: 3.2
µ
s
3.2
µ
s / 0.2
µ
s = 16
HVTHR value = H'10 (16)
In general, to detect Hsync pulses continuously, set the HVTHR value so that 2.35-
µ
s equalizing
pulses can be detected. However, if an equalizing pulse at an Hsync pulse position is lost in a
weak field, a Hsync-Vsync phase-difference error will occur, and the field will not be detected
correctly. In such a weak field, this error can be prevented by eliminating 2.35-
µ
s equalizing
pulses. Figure 27.5 shows the timing when a phase-difference error occurs.