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AD9992

Rev. C | Page 56 of 92

COMPLETE EXPOSURE/READOUT OPERATION

USING PRIMARY COUNTER AND GPO SIGNALS

Figure 65 demonstrates a typical expose/read cycle while exercising

the GPO signals. Using a 3-field CCD with an exposure time

that is greater than one field but less than two fields in duration

requires a total of five fields for the entire exposure/readout

operation. Other exposure times and other CCD field config-

urations require modification of these example settings.

Note that, if the MODE registers are changed to VD updated, as

shown in the MODE Registers section and in Figure 53, the

MODE update is delayed by one additional field. This should be

accounted for in selecting the number of fields to cycle and the VD

location to write to the MODE registers.

The primary counter is used to control the masking of VSG

and SUBCK during exposure/readout. The PRIMARY_MAX

used for exposure and readout. In this example,

PRIMARY_MAX = 5.

The SUBCK masking should not occur immediately at

the next VD edge (Step 2) because this would define an

exposure time that begins in the previous field. Write to

the PRIMARY_DELAY register to delay the masking of

VSG and SUBCK pulses in the first exposure field. In this

example, MASKDELAY = 1.

Write to the SUBCKMASK_NUM register (Address 0x74)

to specify the number of fields to mask SUBCK while the

CCD data is read. In this example, SUBCKMASK_NUM = 4.

Write to the SGMASK_NUM register (Address 0x74) to

specify the number of fields to mask VSG outputs during

exposure. In this example, SGMASK_NUM = 1.

Write to the PRIMARY_ACTION register (Address 0x70)

to trigger the GP1 (STROBE), GP2 (MSHUT), and GP3

(VSUB) signals and to start the expose/read operation.

Write to the MODE registers to configure the next five

fields. The first two fields during exposure are the same as

the current draft mode fields, and the following three fields

are the still-frame readout fields. The register settings for

the draft mode field and the three readout fields are

previously programmed. Note that if the MODE registers

are changed to VD updated, only one field of exposure

should be included (the second one) because the MODE

settings will be delayed an extra field.

VD/HD falling edge updates the serial writes from 1.

GP3 (VSUB) output turns on at the field/line/pixel specified.

VSUB Example 1 and Example 2 use GP3TOG1_FD = 1.

GP1 (STROBE) output turns on and off at the location

specified.

GP2 (MSHUT) output turns off at the location specified.

The next VD falling edge automatically starts the first

read field.

The next VD falling edge automatically starts the second

read field.

The next VD falling edge automatically starts the third

read field.

Write to the MODE register to reconfigure the single draft

mode field timing. Note that if the MODE registers are

changed to VD updated, this write should occur one field

earlier.

10. VD/HD falling edge updates the serial writes from Step 9.

VSG outputs return to draft mode timing. SUBCK output

resumes operation. GP2 (MSHUT) output returns to the on

position (active or open). GP3 (VSUB) output returns to

the off position (inactive)

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