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5.0

SNAPSHOT MODE

The LM9627 is capable of capturing a single frame of an image

under hardware or software control, with or without the aid of an

external

shutter.

Two

registers,

SNAPSHOTMODE0

&

SNAPSHOTMODE1, are provided to program, monitor and con-

trol all snapshot sequences.

5.1

Software Controlled Snapshots

The snapshot mode events can be software controlled by writing

to and reading from the snapshot mode registers over the I

compatible interface.

5.2

Hardware Controlled Snapshots

Two dedicated pins are provided on the LM9627, snapshot &

extsync, allowing the snapshot mode events to be controlled by

hardware. The snapshot pin must be enabled by writing to the

SnapEnable bit of the MCFG0 register.

5.3

Auto Snapshot Mode

In auto snapshot mode (see figure 20), upon the receipt of a

control circuit will set the FTriggerEN bit and generate an inter-

nal TRIGGER signal (see figure 19), thus resetting the array one

row at a time. At end of the reset cycle the timing and control cir-

cuit will signal the shutter to open via extsync pin or FtSync bit.

At the end of the programmed integration time the shutter will be

signalled to close, and the pixel read-out will commence as

shown in figure 18a. At the end of the read-out sequence the

FTriggerEN will be automatically reset and the sensor will return

to video capture mode as shown in figure 20.

If an external shutter is not available then at least two frames

need to be taken so that the pixels can be integrated over one

frame as shown in Figure 18b.

To use auto snapshot mode the

SsEngage bit of the

SNAPSHOTMODE1 register must be set to zero.

Note 1:

This wave form shows the snapshot pin programmed to the default pulse mode.

Note 2:

The irq pulse is taken low when the snapshot trigger interrupt flag (SsTrigFlag) in the snapshot mode1 (SNAPMODE1) register is read.

Note 3:

The irq pulse is taken low when the snapshot trigger interrupt flag (SsRdFlag) in the snapshot mode1 (SNAPMODE1 ) register is read.

Figure 18. Snapshot Mode

Start Snapshot Sequence

Start of Array Reset Frames

Open Shutter

Close shutter & start read-out

Read-out complete

FTriggerEn

snapshot or FTriggerNow

extsync or FtSync

FtBusy

Array reset,

irq

programmable 1 to 4 frames

Capture

Data

read-out

image

note1

note2

note 3

Start Snapshot sequence

Start of Array Reset Frames

Integration Start

Start Read-out

Read-out Complete

FTriggerEn

snapshot or FTriggerNow

extsync or FtSync

FtBusy

Bold external pins

italic register bits

Array reset,

irq

programmable 1 to 4 frames

Capture

Data

read-out

image

note 1

note 2

note 3

a) With External Shutter

b) Without External Shutter