Rev. 1.0, 02/00, page 775 of 1141
Csync
VVTH
SEPV
521
522
523
524
0
1
2
3
4
5
6
7
8
AFCV
1/2 AFCH
(V sampling clock)
Digital H separation
counter
V complement and
mask counter
Figure 27.10 AFCV Generation Timing When V Complement Function Is Enabled
(for NTSC)
27.2.6
Field Detection Window Register (FWIDR)
0
0
0
0
0
1
1
1
7
W
FWID0
1
—
—
6
—
—
5
—
—
4
—
—
3
W
FWID3
2
W
FWID2
1
W
FWID1
Bit :
Initial value :
R/W :
The FWIDR is a 4-bit write-only register for specifying the field detection window timing in units
of 16
×
fh (fh: horizontal sync signal frequency). The field detection window signal is reset to 0
when the AFC dividing counter value matches the FWIDR value, and the signal is again set to 1
when 1/2 the Hsync signal period has passed. At a rising edge of the AFCV signal while the field
detection window signal is 1, the field is determined as an odd one, and the field detection flag
(FLD) is set to 1. At a rising edge of the AFCV signal while the field detection window signal is 0,
the field is determined as an even one, and the FLD is cleared to 0. The value set to the FWIDR
depends on the setting of the V complement function control (VCMPON) bit (bit 4) of the
SEPCR. When the VCMPON is cleared to 0, that is, when the V complement function is not
operating, the FWIDR must be set so that the rising edge of the SEPV signal, which is generated
when the V separation counter value reaches the specified threshold value, comes to the center of
the field detection window period. When the VCMPON is set to 1, that is, when the V
complement function is operating, the FWIDR must be set so that the dividing counter overflow
timing comes to the center of the field detection window period. When reset, the FWIDR is
initialized to H'F0.
(1) Bit 0 of SEPACR Register