Datasheet

AD9923A
Rev. A | Page 20 of 84
Individual HBLK Patterns
The HBLK programmable timing shown in Figure 26 is similar
to CLPOB and PBLK; however, there is no start polarity control.
Only the toggle positions are used to designate the start and end
positions of the blanking period. Additionally, there is a polarity
control register, HBLKMASK, that designates the polarity of the
horizontal clock signals during the blanking period. Setting
HBLKMASK high sets H1 = H3 = high and H2 = H4 = low
during blanking, as shown in Figure 27. As with CLPOB and
PBLK registers, HBLK registers are available in each V-sequence,
allowing different blanking signals to be used with different
vertical timing sequences.
Note that 8189 is the recommended setting for any unused
HBLK toggle locations on the AD9923A, regardless of the
setting for HBLKALT. 8190 and 8191 are not valid settings for
HBLK toggle positions that are unused and causes undesired
HBLK toggle activity.
Generating Special HBLK Patterns
There are six toggle positions available for HBLK. Normally,
only two of the toggle positions are used to generate the
standard HBLK interval. However, additional toggle positions
can be used to generate special HBLK patterns, as shown in
Figure 28. The pattern in this example uses all six toggle
positions to generate two extra groups of pulses during the
HBLK interval. By changing the toggle positions, different
patterns can be created.
Table 13. HBLK Pattern Registers
Register
Length
(Bits) Range Description
HBLKMASK 1 High/low Masking polarity for H1, H3, HL (0 = mask low, 1 = mask high)
HBLKALT 3 0 to 7 alternation modes Enables different odd/even alternation of HBLK toggle positions
0: disable alternation (HBLKTOGE1 to HBLKTOGE6 registers are used for each line)
1: TOGE1 and TOGE2 odd lines, TOGE3 to TOGE6 even lines
2: TOGE1 and TOGE2 even lines, TOGE3 to TOGE6 odd lines
3: TOGE1 to TOGE6 even lines, TOGO1 to TOGE6 odd lines (FREEZE/RESUME not
available)
4 to 7: HBLKSTART, HBLKEND, HBLKLEN, and HBLKREP registers are used for each line
HBLKTOGE1 13 0 to 8189 pixel location HBLK first toggle position (for even lines only when HBLKALT = 3)
HBLKTOGE2 13 0 to 8189 pixel location HBLK second toggle position (for even lines only when HBLKALT = 3)
HBLKTOGE3 13 0 to 8189 pixel location HBLK third toggle position (for even lines only when HBLKALT = 3)
HBLKTOGE4 13 0 to 8189 pixel location HBLK fourth toggle position (for even lines only when HBLKALT = 3)
HBLKTOGE5 13 0 to 8189 pixel location Fifth toggle position, even lines (HBLKSTART when HBLKALT = 4 to 7)
HBLKTOGE6 13 0 to 8189 pixel location Sixth toggle position, even lines (HBLKEND when HBLKALT = 4 to 7)
HBLKLEN 13 0 to 8189 pixels HBLK pattern length, only used when HBLKALT = 4 to 7
HBLKREP 8 0 to 255 repetitions Number of HBLK pattern repetitions, only used when HBLKALT = 4 to 7
HBLKTOGO1 13 0 to 8189 pixel location First toggle position for odd lines when HBLKALT = 3 (usually VREPA_3)
HBLKTOGO2 13 0 to 8189 pixel location Second toggle position for odd lines when HBLKALT = 3 (usually VREPA_4)
HBLKTOGO3 13 0 to 8189 pixel location Third toggle position for odd lines when HBLKALT = 3 (usually FREEZE1)
HBLKTOGO4 13 0 to 8189 pixel location Fourth toggle position for odd lines when HBLKALT = 3 (usually RESUME1)
HBLKTOGO5 13 0 to 8189 pixel location Fifth toggle position for odd lines when HBLKALT = 3 (usually FREEZE2)
HBLKTOGO6 13
0 to 8189 pixel location
Sixth toggle position for odd lines when HBLKALT = 3 (usually RESUME2)
HD
HBLK
BASIC HBLK PULSE IS GENERATED USING HBLKTOGE1 AND HBLKTOGE2 REGISTERS (HBLKALT = 0).
BLANK BLANK
HBLKTOGE1 HBLKTOGE2
05586-024
Figure 26. Typical Horizontal Blanking (HBLK) Pulse Placement