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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
556 of 808
NXP Semiconductors
UM10360
Chapter 29: LPC17xx Analog-to-Digital Converter (ADC)
6.3 Accuracy vs. digital receiver
The ADC function must be selected via the PINSEL registers in order to get accurate
voltage readings on the monitored pin. The PINMODE should also be set to the mode for
which neither pull-up nor pull-down resistor is enabled. For a pin hosting an ADC input, it
is not possible to have a have a digital function selected and yet get valid ADC readings.
An inside circuit disconnects ADC hardware from the associated pin whenever a digital
function is selected on that pin.
6.4 DMA control
A DMA transfer request is generated from the ADC interrupt request line. To generate a
DMA transfer the same conditions must be met as the conditions for generating an
interrupt (see
and
Remark:
If the DMA is used, the ADC interrupt must be disabled in the NVIC.
For DMA transfers, only burst requests are supported. The burst size can be set to one in
the DMA channel control register (see
). If the number of ADC channels is
not equal to one of the other DMA-supported burst sizes (applicable DMA burst sizes are
1, 4, 8 - see
), set the burst size to one.
The DMA transfer size determines when a DMA interrupt is generated. The transfer size
can be set to the number of ADC channels being converted (see
Non-contiguous channels can be transferred by the DMA using the scatter/gather linked
lists (see
).