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AD9898

Special Vertical Sweep Mode Operation

The AD9898 contains a special mode of vertical timing operation

called sweep mode. This mode is used to generate a continu-

ous number of repetitive vertical pulses that span multiple HD

lines. One example of when this mode may be needed is the

start of the CCD readout operation. At the end of the image

exposure, but before the image is transferred by the sensor gate

pulses, the vertical interline CCD registers should be cleared of

all charge. The charge can be shifted out quickly with a long

series of pulses on the V1–V4 outputs. This operation will span

multiple HD line lengths.

Normally the sequences are contained within one HD line length,

but with the sweep mode enabled, the HD boundaries will be

ignored until the region is finished. The special vertical sweep

mode operation is only output in CCD Region0 and CCD

Region3. (See Figures 33 and 34.) The SVREP_MODE register

located at control Address 0x0A is used to enable and configure

the special sweep mode operation as described in Table XVIII.

The maximum number of repeats in each region is 2048

while operating in this mode using the SVREP0 and SVREP3

Mode_Reg(4) registers.

Table XVIII. Description of SVREP_MODE Register

SVREP_MODE

Description of Sweep Mode Operation

Normal Vertical Timing Operation in All CCD Regions

Special Vertical Sweep Mode Timing Output in CCD Region0 Only

Special Vertical Sweep Mode Timing Output in CCD Region3 Only

Special Vertical Sweep Mode Timing Output in CCD Region0 and CCD Region3

V1–V4

Figure 31. NonOverlapping Example for Normal Vertical Timing Operation with SVREP_MODE = 0 and VTPREPx = 4

V1–V4

NOT OUTPUT BECAUSE THE 8TH

REPETITION OVERLAPS WITH HD

Figure 32. Overlapping Example for Normal Vertical Timing Operation with SVREP_MODE = 0 and VTPREPx = 8

V1–V4

CCD REGION0

SCP0

SCP1 = 3

Figure 33. Sweep Mode Timing Example with SVREP_MODE = 1 and SVREP0 = 28

V1–V4

CCD REGION3

SCP3

SCP4 = 3

Figure 34. Sweep Mode Timing Example with SVREP_MODE = 2 and SVREP3 = 28

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