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CHAPTER 11 A/D CONVERTER (Successive approximation type)
11.5 Conversion Data Protection Function
The A/D converter of the MB91F109 has a conversion data protection function that
features continuous conversion using DMAC and securing multiple data items.
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Conversion Data Protection Function
The A/D converter has only one conversion data register. That means that in continuous
conversion mode, new conversion data overwrites the previously stored data in the register
each time one cycle of A/D conversion is finished. The A/D converter has a function to prevent
this problem. If the previously stored data has not been transferred to memory using the DMAC
when conversion is finished, the A/D converter refrains from storing new conversion data in the
register and stops instead.
The A/D converter is released from the stop state after previous data is transferred to memory in
DMA transfer mode.
If previous data has already been transferred when current conversion is finished, the A/D
converter continues conversion without stopping.
<Notes>
The conversion data protection function is affected by the ADCS INT and INTE bits.
The function works only when interrupts are enabled (INTE = 1).
The function does not work when interrupts are disabled (INTE = 0), and conversion data
overwrites the register successively and previous data is lost if A/D conversion is performed
continuously.
If DMA transfer is not used when interrupts are enabled (INTE = 1), the INT bit is not cleared
and therefore the data protection function works and puts the A/D converter in the stopped
state. In this case, clearing the INT bit in the interrupt sequence releases the A/D converter
from the stopped state.
If interrupts are disabled while the A/D converter pauses in DMA operation mode, the A/D
converter works and may update the data register before previous data is transferred.
Restarting the A/D converter in stopped state may lead to loosing the held data.
Figure 11.5-1 shows the Workflow of the data protection function when DMA transfer is used.