
AD9920A
Rev. B | Page 27 of 112
Register
Length
(Bits)
Range
Description
HBLKSTARTA
13
0 to 8191 pixel location
HBLK Repeat Area Start Position A for HBLK Mode 1. Set to 8191 if not used.
HBLKSTARTB
13
0 to 8191 pixel location
HBLK Repeat Area Start Position B for HBLK Mode 1. Set to 8191 if not used.
HBLKSTARTC
13
0 to 8191 pixel location
HBLK Repeat Area Start Position C for HBLK Mode 1. Set to 8191 if not used.
HBLKALT_PAT0
3
0 to 5 even repeat area
HBLK Mode 1, Repeat Area 0 pattern for odd lines. Selected from previously
defined even line repeat areas.
HBLKALT_PAT1
3
0 to 5 even repeat area
HBLK Mode 1, Repeat Area 1 pattern for odd lines.
HBLKALT_PAT2
3
0 to 5 even repeat area
HBLK Mode 1, Repeat Area 2 pattern for odd lines.
HBLKALT_PAT3
3
0 to 5 even repeat area
HBLK Mode 1, Repeat Area 3 pattern for odd lines.
HBLKALT_PAT4
3
0 to 5 even repeat area
HBLK Mode 1, Repeat Area 4 pattern for odd lines.
HBLKALT_PAT5
3
0 to 5 even repeat area
HBLK Mode 1, Repeat Area 5 pattern for odd lines.
1 PIXEL
MASK LEVEL = HIGH
MASK LEVEL = LOW
BLANKING
PHASE 1
PHASE 3
PHASE 2
INTERNAL
DIGITAL
CLOCK
MASTER
BLANKING
SIGNAL
H1/H2
H5/H6
H7/H8
1 PIXEL
A3
A2
A1
A
B
B3
B2
B1
06
87
8-
0
32
Figure 33. Example of Correct HBLK Behavior
HBLK Fine Retime Control
Figure 33 shows the desired HBLK behavior for all three phases
when the internal digital clock is located before the Phase 3 rising
edge.
Figure 34 shows the effect of changing the internal clock
phase (changing SHDLOC) to a different location. This causes
incorrect blanking on Phase 1 and Phase 2.
An additional set of register bits is available for use during
3-phase HCLK mode to provide fine adjustment of each HCLK
phase during the HBLK interval. The fine retime bits (Address 0x35,
Bits[23:20]) allow for the adjustment of the correct number of
HCLK cycles during the HBLK interval.
Figure 35 shows how the fine retime bits for Phase 1 and Phase 2
are used to generate the correct blanking behavior, matching the
be used based on the location of the HBLK toggle positions, the
location of the internal digital clock, and the masking polarity
of the different HCLK phases. By using the fine retime bits, the
exact pulse behavior for each HCLK phase can be generated.