AD9920ABBCZ datasheet(40/112 Pages) AD

40 / 112 page

AD9920A

Rev. B | Page 40 of 112

Using the LASTREPLEN_EN Register

The LASTREPLEN_EN register (Address 0x00, Bits[19:16] in the

V-sequence registers) is used to enable a separate pattern length

to be used in the final repetition of several pulse repetitions. If a

different last length is not required, it is still recommended that

the LASTREPLEN_EN register bits be set high (enabled) and that

the LASTREPLEN_A, LASTREPLEN_B, LASTREPLEN_C, and

LASTREPLEN_D registers be set to a value equal to the VLENA,

VLENB, VLENC, and VLEND register values, respectively.

Generating Line Alternation for V-Sequences and HBLK

During low resolution readout, some CCDs require a different

number of vertical clocks on alternate lines. The AD9920A can

support this requirement by using the VREP registers. These

registers allow a different number of V-pattern group repetitions

to be programmed on odd and even lines. Only the number of

repeats can be different in odd and even lines if the V-pattern

group remains the same. There are separate controls for the

assigned Group A, Group B, Group C, and Group D patterns.

All groups can support odd and even line alternation. Group A

uses the VREPA_1 and VREPA_2 registers; Group B, Group C,

and Group D use the corresponding VREPx_ODD and

VREPx_EVEN registers. Using the additional VREPA_3 and

VREPA_4 registers, Group A can also support three-line and

four-line alternation.

As described in the Generating HBLK Line Alternation section,

the HBLK signal can be alternated for odd and even lines. Figure 50

shows an example of V-pattern group repetition alternation and

HBLK Mode 0 alternation used together.

XV1

XV2

XV24

HBLK

TOGE1

TOGE2

TOGO1

TOGO2

TOGE1

TOGE2

NOTES

1. THE NUMBER OF REPEATS FOR V-PATTERN GROUPS A/B/C/D CAN BE ALTERNATED ON ODD AND EVEN LINES.

2. GROUP A ALSO SUPPORTS 3- AND 4-LINE ALTERNATION USING THE ADDITIONAL VREPA_3 AND VREPA_4 REGISTERS.

3. THE HBLK TOGGLE POSITIONS CAN BE ALTERNATED BETWEEN ODD AND EVEN LINES TO GENERATE DIFFERENT HBLK PATTERNS.

VREPA_1 = 2

(OR VREPB/C/D_EVEN = 2)

VREPA_2 = 5

(OR VREPB/C/D_ODD = 5)

VREPA_1 = 2

(OR VREPB/C/D_EVEN = 2)

Figure 50. Odd/Even Line Alternation of V-Pattern Group Repetitions and HBLK Toggle Positions

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