AD9929BBCZ datasheet(31/64 Pages) AD

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AD9929

Rev. A | Page 31 of 64

H1 AND H2 BLANKING

The AD9929 provides three options for controlling the period

where H1 and H2 pulses get blanked. These options are normal

H blanking, selective positioning for 2 H1 and H2 outputs, and

extended blanking. In all cases, HBLKMASK is used to set the

polarity of H1 during the blanking period. Table 21 describes

the registers used to control H blanking.

Normal H-Blanking

For normal H-blanking operation, HPULSECNT = 0 and

BLKMASK = 0 or 1. The HBLKPOS register isn’t used in this

mode. Figure 27 shows one example where HBLKMASK = 0

and H1 and H2 are blanked while HD is low.

Selective Positioning for Two H1 and H2 Outputs

For selective positioning operation, HPULSECNT = 1 and

HBLKMASK = 0 or 1. In this mode, two H1 pulses are output

during the blanking period. The location of these two pulse is

set using the HBLKPOS register, as shown in Figure 28.

Extended Blanking

Extended blanking is enabled by setting HBLKEXT = 1. The

HBLKEXT register uses the 9-bit BL counter to suspend

operation of the HD and HL counters. This delays the blanking

period by the length set in the BLLEN register, as shown in

Figure 29.

Table 21. H1 Blanking Registers

Name

Bit

Width

Description

HBLKMASK

Control (0x01)

Masking Polarity for H1 during Blanking Period1

(0 = Low, 1 = High)

HPULSECNT

Control (0x0A)

H Pulse Control during Blanking Period

HBLKEXT

Control (0x0A)

(0 = No Output during Blanking,1 = Output during Blanking ) H Pulse Blanking Extends

Control2

(0 = Extended Blanking Disabled, 1 = Extended Blanking Enabled)

H1BLKRETIME

Control (0x03)

Retimes the H1 HBLK to Internal Clock

(0 = Retiming Disabled, 1 = Retiming Enabled)

HBLKHPOS

Sys_Reg(11)

H1 Pulse ON Position during Blanking Period

1 H2 is always the opposite polarity of H1.

2 The HBLKEXT extend control extends the blanking period by the number of counts set in the BLLEN register for the 9-bit BL counter.

HBLK

(INTERNAL)

HDRISE

NOTES

1. THE RISING EDGE OF HBLK IS ALWAYS THE SAME AS HDRISE

Figure 27. Normal H-Blanking Operation HBLKMASK = 0, HPULSECNT = 0, HBLKHPOS = XXX

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