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READOUT MODES

By default, the readout of the pixel array does not require

any user interaction. The sequencer initiates the readout as

soon as integration ends and the entire readout is done

autonomously. This is the default readout mode.

Optionally, the frame readout can be controlled

externally. This requires configuring the TRIG_RD input as

a frame or line trigger. Table 11 below lists the parameters

that control the triggered readout operation.

Table 11. TRIGGERED READOUT PARAMETERS

Description

frame_trigger_en

Start the frame readout upon assertion of TRIG_RD when enabled.

This configuration has priority over line_trigger_en.

frame_trigger_mode

Only valid for frame triggered readout modes.

‘0’: Regular frame triggered mode: The sensor starts the readout of one frame upon a rising trigger

edge

‘1’: The sequencer continues frame grabbing as long as the trigger is asserted.

line_trigger_en

Start the readout of one line upon assertion of TRIG_RD when enabled. Only one line is read out for

each trigger assertion.

Note that contexts_reg.frames determines how many

frames can be read out. This implies that the sequencer will

not accept any new trigger once the number of

contexts_reg.frames have been read out. If this is not

desired, frames should be configured to 0.

FRAME TRIGGERED READOUT

Figure 21. Frame Triggered Readout Mode

Idle

Integrating

Idle

Integrating

Readout

EFOT

Frame N

Frame N + 1

Exposure State

TRIG_INT

TRIG_RD

(No effect on falling edge

)

SFOT

EFOT

Reset

EFOT

SFOT

EFOT

Reset

integration length

= Start of New Line

= Readout

XGS 12000 supports two frame triggered readout options,

configurable in the frame_trigger_mode register (refer to

Table 11).

frame_trigger_mode = 0

In a global shutter mode, the integration is ended by the

EFOT. In a non−triggered readout mode, the readout is

initiated automatically after the EFOT operations. In frame

triggered mode, the Sequencer will not start the readout, but

instead it waits until the frame−trigger gets asserted. Once

an event (rising of falling depending on the configured

polarity) is detected the readout starts and the image is read

out line after line.

Note that the trigger assertion is latched and served at the

first coming internal new line reference (internal time base).

As a consequence one may observe a trigger latency up to a

line time.

Frame triggered readout can be combined with triggered

integration modes.

frame_trigger_mode = 1

In this mode, the trigger acts as an external sequencer

enable signal. An event (rising or falling depending on the

configured polarity) starts the frame readout. After this first

frame, the sequencer continues running, cycling through the

active contexts, if more than one context is enabled. The end

condition

depends

the

value

given

contexts_reg.frames:

• contexts_reg.frames > 0: The Sequencer continues

running and reads out the given amount of frames, after

which it returns to the WAIT_ON_TRIGGER state.

After the readout, the sequencer is waiting for another

trigger, after which a new sequence is initiated. Note

that a new batch of frames shall be read out in case the

trigger is asserted at the end of the previous batch.

• contexts_reg.frames = 0: The Sequencer continues

running as long as the TRIG_RD is asserted. Once the

trigger is deasserted, the Sequencer returns to the

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