XC886/888CLM
Analog-to-Digital Converter
User’s Manual
16-5
V1.3, 2010-02
ADC, V 1.0
Synchronization Phase
t
SYN
One
f
ADCI
period is required for synchronization between the conversion start trigger
(from the digital part) and the beginning of the sample phase (in the analog part). The
BUSY and SAMPLE bits will be set with the conversion start trigger.
Sample Phase
t
S
During this period, the analog input voltage is sampled. The internal capacitor array is
connected to the selected analog input channel and is loaded with the analog voltage to
be converted. The analog voltage is internally fed to a voltage comparator. With the
beginning of the sampling phase, the SAMPLE and BUSY flags in register GLOBSTR
are set. The duration of this phase is common to all analog input channels and is
controlled by bit field STC in register INPCR0:
t
S
= (2 + STC)
×
t
ADCI
(16.1)
Conversion Phase
During the conversion phase, the analog voltage is converted into an 8-bit or 10-bit
digital value using the successive approximation technique with a binary weighted
capacitor network. At the beginning of the conversion phase, the SAMPLE flag is reset
(to indicate the sample phase is over), while the BUSY flag continues to be asserted. The
BUSY flag is deasserted only at the end of the conversion phase with the corresponding
source interrupt (of the source that started the conversion) asserted.
Write Result Phase
t
WR
At the end of the conversion phase, the corresponding channel interrupt (of the
converted channel) is asserted three
f
ADCI
periods later, after the limit checking has been
performed. The result interrupt is asserted, once the conversion result has been written
into the target result register.
*