ST7PLITEU09M3TR View Datasheet(PDF) - STMicroelectronics
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Description
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ST7PLITEU09M3TR Datasheet PDF : 115 Pages
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ST7LITEU05 ST7LITEU09
10-BIT A/D CONVERTER (ADC) (Cont’d)
11.3.3.2 Digital A/D Conversion Result
The conversion is monotonic, meaning that the re-
sult never decreases if the analog input does not
and never increases if the analog input does not.
If the input voltage (VAIN) is greater than VDD (high-
level voltage reference) then the conversion result
is FFh in the ADCDRH register and 03h in the AD-
CDRL register (without overflow indication).
If the input voltage (VAIN) is lower than VSS (low-lev-
el 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 AD-
CDRL registers. The accuracy of the conversion is
described in the Electrical Characteristics Section.
RAIN 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.
11.3.3.3 A/D Conversion Phases
The A/D conversion is based on two conversion
phases:
■ Sample capacitor loading [duration: tSAMPLE]
During this phase, the VAIN input voltage to be
measured is loaded into the CADC sample
capacitor.
■ A/D conversion [duration: tHOLD]
During this phase, the A/D conversion is
computed (8 successive approximations cycles)
and the CADC sample capacitor is disconnected
from the analog input pin to get the optimum
analog to digital conversion accuracy.
■ The total conversion time:
tCONV = tSAMPLE + tHOLD
While the ADC is on, these two phases are contin-
uously repeated.
At the end of each conversion, the sample capaci-
tor is kept loaded with the previous measurement
load. The advantage of this behaviour is that it
minimizes the current consumption on the analog
pin in case of single input channel measurement.
11.3.3.4 A/D Conversion
The analog input ports must be configured as in-
put, no pull-up, no interrupt. Refer to the “I/O ports”
chapter. Using these pins as analog inputs does
not affect the ability of the port to be read as a logic
input.
In the ADCCSR register:
– Select the CS[2:0] bits to assign the analog
channel to convert.
ADC Conversion mode
In the ADCCSR register:
Set the ADON bit to enable the A/D converter and
to start the conversion. From this time on, the ADC
performs a continuous conversion of the selected
channel.
When a conversion is complete:
– The EOC bit is set by hardware.
– The result is in the ADCDR registers.
A read to the ADCDRH or a write to any bit of the
ADCCSR register resets the EOC bit.
To read the 10 bits, perform the following steps:
1. Poll EOC bit
2. Read ADCDRL
3. Read ADCDRH. This clears EOC automati-
cally.
To read only 8 bits, perform the following steps:
1. Poll EOC bit
2. Read ADCDRH. This clears EOC automati-
cally.
11.3.3.5 Changing the conversion channel
The application can change channels during con-
version.
When software modifies the CH[2:0] bits in the
ADCCSR register, the current conversion is
stopped, the EOC bit is cleared, and the A/D con-
verter starts converting the newly selected chan-
nel.
11.3.4 Low Power Modes
Note: The A/D converter may be disabled by re-
setting the ADON bit. This feature allows reduced
power consumption when no conversion is need-
ed and between single shot conversions.
Mode
WAIT
HALT
Description
No effect on A/D Converter
A/D Converter disabled.
After wakeup from Halt mode, the A/D Con-
verter requires a stabilization time tSTAB (see
Electrical Characteristics) before accurate
conversions can be performed.
11.3.5 Interrupts
None.
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