MT9P001 Datasheet, PDF (28/48 Pages) ON Semiconductor – CMOS Digital Image Sensor

MT9P001: 1/2.5-Inch 5Mp Digital Image Sensor
Features
usually active during the readout of the previous frame. Therefore, any register changes
that could affect the row time or the set of rows sampled causes the shutter pointer to
start over at the beginning of the next frame.
By default, the following register fields cause a "bubble" in the output rate (that is, the
vertical blank increases for one frame) if they are written in continuous mode, even if the
new value would not change the resulting frame rate:
• Row_Start
• Row_Size
• Column_Size
• Horizontal_Blank
• Vertical_Blank
• Shutter_Delay
• Mirror_Row
• Row_Bin
• Row_Skip
• Column_Skip
The size of this bubble is (SW × ^tROW), calculating the row time according to the new
settings.
The Shutter_Width_Lower and Shutter_Width_Upper fields may be written without
causing a bubble in the output rate under certain circumstances. Because the shutter
sequence for the next frame often is active during the output of the current frame, this
would not be possible without special provisions in the hardware. Writes to these regis-
ters take effect two frames after the frame they are written, which allows the shutter
width to increase without interrupting the output or producing a corrupt frame (as long
as the change in shutter width does not affect the frame time).
Synchronizing Register Writes to Frame Boundaries
Changes to most register fields that affect the size or brightness of an image take effect
on the frame after the one during which they are written. These fields are noted as
“synchronized to frame boundaries” in Table 1: Register List and Default Values on
page 5 in the MT9P0901 register reference. To ensure that a register update takes effect
on the next frame, the write operation must be completed after the leading edge of FV
and before the trailing edge of FV.
As a special case, in Snapshot modes (see “Operating Modes” on page 31), register writes
that occur after FV but before the next trigger will take effect immediately on the next
frame, as if there had been a Restart. However, if the trigger for the next frame in ERS
Snapshot mode occurs during FV, register writes take effect as with continuous mode.
Additional control over the timing of register updates can be achieved by using synchro-
nize_changes. If this bit is set, writes to certain register fields that affect the brightness of
the output image do not take effect immediately. Instead, the new value is remembered
internally. When synchronize_changes is cleared, all the updates simultaneously take
effect on the next frame (as if they had all been written the instant synchronize_changes
was cleared). Register fields affected by this bit are identified in Table 2: Register
Description on page 10 of the MT9P001 register reference.
Fields not identified as being frame-synchronized or affected by synchronize_changes
are updated immediately after the register write is completed. The effect of these regis-
ters on the next frame can be difficult to predict if they affect the shutter pointer.
MT9P001_DS Rev. L 4/15 EN
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