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On-chip peripherals
ST7LITEUS2, ST7LITEUS5
Figure 36.
ADC block diagram
Digital A/D conversion result
The conversion is monotonic, meaning that the result never decreases if the analog input
does not and never increases if the analog input does not.
If the input voltage (V
AIN
) is greater than V
DDA
(high-level voltage reference) then the
conversion result is FFh in the ADCDRH register and 03h in the ADCDRL register (without
overflow indication).
If the input voltage (V
AIN
) is lower than V
SSA
(low-level voltage reference) then the
conversion result in the ADCDRH and ADCDRL registers is 00 00h.
The A/D converter is linear and the digital result of the conversion is stored in the ADCDRH
and ADCDRL registers. The accuracy of the conversion is described in the Electrical
Characteristics Section.
R
AIN
is the maximum recommended impedance for an analog input signal. If the impedance
is too high, this will result in a loss of accuracy due to leakage and sampling not being
completed in the alloted time.
A/D conversion phases
The A/D conversion is based on two conversion phases:
●
Sample capacitor loading [duration: t
SAMPLE
]
During this phase, the V
AIN
input voltage to be measured is loaded into the C
ADC
sample capacitor.
●
A/D conversion [duration: t
HOLD
]
During this phase, the A/D conversion is computed (8 successive approximations
CH2
CH1
EOC SPEED ADON
0
CH0
ADCCSR
AIN0
AIN1
ANALOG TO DIGITAL
CONVERTER
AINx
ANALOG
MUX
D4
D3
D5
D9
D8
D7
D6
D2
ADCDRH
3
D1
D0
ADCDRL
0
0
0
0
SLOW
0
0
R
ADC
C
ADC
HOLD CONTROL
f
ADC
f
CPU
0
1
1
0
DIV 2
DIV 4
SLOW
bit
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