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MS51
Nov. 28, 2019
Page
441
of 491
Rev 1.00
MS51
32K
SE
RIES
TE
CHNICAL RE
F
EREN
CE MA
N
UAL
6.13 12-Bit Analog-To-Digital Converter (ADC)
6.13.1 Overview
The MS51 32K series is embedded with a 12-bit SAR ADC. The ADC (analog-to-digital converter)
allows conversion of an analog input signal to a 12-bit binary representation of that signal. The MS51
32K series is selected as 8-channel inputs in single end mode. The internal band-gap voltage 1.22 V
also can be the internal ADC input. The analog input, multiplexed into one sample and hold circuit,
charges a sample and hold capacitor. The output of the sample and hold capacitor is the input into the
converter. The converter then generates a digital result of this analog level via successive
approximation and stores the result in the result registers. The ADC controller also supports
continuous conversion and storage result data into XRAM.
6.13.2 Functional Description
ADC Operation
6.13.2.1
0000
0001
0010
0011
0100
0101
0110
0111
1000
VBG
ADCHS[3:0]
ADCEX
1 2- bit SAR
ADC
ADCRH
ADCRL
ADCF
ADC result
comparator
External
Trigger
V
DD
ADCEN
ADCS
ADC XRAM Control
ADCBAH
ADCSN
XRAM
(Auxiliary RAM)
ADC Interrupt
12
ADC flag
Re-trigger
V
REF
V
R
E
F
A
D
C
V
D
D
STADC
ADC_CH0
ADC_CH1
ADC_CH2
ADC_CH3
ADC_CH4
ADC_CH5
ADC_CH6
ADC_CH7
A
D
C
c
o
n
v
e
rs
io
n
s
ta
rt
1001
ADC_CH9
ADC_CH10
1011
ADC_CH11
1100
ADC_CH12
1101
ADC_CH13
1110
ADC_CH14
1111
ADC_CH15
1010
Figure 6.13-1 12-bit ADC Block Diagram
Before ADC operation, the ADC circuit should be enabled by setting ADCEN (ADCCON1.0). This
makes ADC circuit active. It consume extra power. Once ADC is not used, clearing ADCEN to turn off
ADC circuit saves power.
The ADC analog input pin should be specially considered. ADCHS[2:0] are channel selection bits that
control which channel is connected to the sample and hold circuit. User needs to configure selected
ADC input pins as input-only (high impedance) mode via respective bits in PxMn registers. This
configuration disconnects the digital output circuit of each selected ADC input pin. But the digital input
circuit still works. Digital input may cause the input buffer to induce leakage current. To disable the
digital input buffer, the respective bits in AINDIDS0 should be set. Configuration above makes