Datasheet

MLX90640 32x24 IR array
Datasheet
Page 12 of 60
REVISION 11 – 3 AUGUST 2018
10.3.
10.3.10.3.
10.3. Measurement
MeasurementMeasurement
Measurement mode
modemode
mode
In this mode the measurements are constantly running. Depending on the selected frame rate Fps in the control
register, the data for IR pixels and Ta will be updated in the RAM each


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second. In this mode the external microcontroller
has full access to the internal registers and memories of the device.
10.4.
10.4.10.4.
10.4. Refresh rate
Refresh rateRefresh rate
Refresh rate
The refresh rate is configured by “Control register 1” (0x800D) i.e. if “Refresh rate control” = 011  4Hz this would mean
that each 250ms a new subpage data is available in the RAM.
NOTE: It is possible to program the desired refresh rate into device EEPROM eliminating the necessity to reconfigure the
device every time it is powered on. The corresponding EEPROM cell is at address 0x240C (see Table 8)
Which subpage is updated is indicated by the “Last measured subpage” field.
It is important to read both subpages as the necessary information for the Ta calculations is only available by combining the
data from both subpages i.e. the Ta is refreshed with an update speed twice as low as the one set in “Refresh rate control”.
When a complete new data set (subpage) is available, a dedicated bit is set to indicate this – bit 3 “New data available in
RAM” in “Status register” (0x8000). It is up to the customer to reset the bit once the data has been read.
Figure 6 Refresh rate timing
Subpage 0
Subpage 1
Subpage 0
Subpage 1
Refresh rate control = 011b (4Hz)
250ms 250ms 250ms 250ms
Set bit “New data available in RAM”