AD9920ABBCZ datasheet(63/112 Pages) AD

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AD9920A

Rev. B | Page 63 of 112

FIELD COUNTERS

The AD9920A contains three field counters (primary, secondary,

and mode). When these counters are active, they increment with

each VD cycle. The mode counter is the field counter used with

the mode register to control the vertical timing signals (see the

Mode Registers section).

The primary and secondary counters are more flexible and are

generally used for shuttering signal applications. Both the primary

and secondary counters have several modes of operation that

are selected by Address 0x70. These modes are as follows:

•

Normal (single count)

•

RapidShot (repeating count)

•

ShotTimer (delayed count)

•

ShotTimer with RapidShot

•

Manual exposure

•

Manual readout

•

Force to idle

The primary counter regulates the expose and read actions

by regulating the SUBCK and VSG signals. In addition, if the

RapidShot feature is used with the primary counter, the SUBCK

and VSG masking automatically repeats as necessary for multiple

expose/read cycles. The secondary counter has no effect on the

SUBCK or VSG signal. Both counters can be used to regulate

the general-purpose signals described in the General-Purpose

Outputs (GPOs) section.

Table 44. Primary/Secondary Field Counter Registers (Address 0x70, Address 0x71, and Address 0x72)

Length (Bits)

Description

PRIMARY_ACTION

0 = idle, no counter action. GPO signals can still be controlled using polarity or by setting the

appropriate GP_PROTOCOL register to 1.

SECOND_ACTION

1 = activate counter. Single cycle of counter from 1 to counter maximum value and then return to

idle state.

2 = RapidShot. After reaching the maximum counter value, the counter wraps and repeats until reset.

3 = ShotTimer. Active single cycle of counter after added delay of n fields (use the corresponding

DELAY register).

4 = ShotTimer with RapidShot. Same as RapidShot (SECOND_ACTION register = 2) but with an added

delay of n fields between each repetition.

5 = manual exposure. Primary counter stays in exposure until manual readout or reset to idle.

This mode keeps the SUBCK and VSG pulses masked indefinitely.

6 = manual readout. Primary counter switches to readout (VSG pulses becomes active).

7 = force to idle.

PRIMARY_MAX

Primary counter maximum value.

SECOND_MAX

Secondary counter maximum value.

VDHD_MASK

Mask VD/HD during counter operation.

PRIMARY_DELAY

ShotTimer. Number of fields to delay before the next primary count (exposure) starts. If using

ShotTimer with RapidShot, the delay value is used between each repetition.

PRIMARY_SKIP

When using ShotTimer with RapidShot, use the primary delay value only before the first count (exposure).

SECOND_DELAY

ShotTimer. Number of fields to delay before the next secondary count starts. If using ShotTimer with

RapidShot, the delay value is used between each repetition.

SECOND_SKIP

When using ShotTimer with RapidShot, use the secondary delay value only before the first count.

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