Comparator_A Operation
23-7
Comparator_A
23.2.7 Comparator_A Used to Measure Resistive Elements
The Comparator_A can be optimized to precisely measure resistive elements
using single slope analog-to-digital conversion. For example, temperature can
be converted into digital data using a thermistor, by comparing the thermistor’s
capacitor discharge time to that of a reference resistor as shown in
Figure 23−5. A reference resister Rref is compared to Rmeas.
Figure 23−5. Temperature Measurement System
+
−
CA0
CCI1B
Capture
Input
Of Timer_A
+
−
Rmeas
Rref
Px.x
Px.y
0.25xV
CC
The MSP430 resources used to calculate the temperature sensed by Rmeas
are:
-
Two digital I/O pins to charge and discharge the capacitor.
-
I/O set to output high (V
CC
) to charge capacitor, reset to discharge.
-
I/O switched to high-impedance input with CAPDx set when not in use.
-
One output charges and discharges the capacitor via Rref.
-
One output discharges capacitor via Rmeas.
-
The + terminal is connected to the positive terminal of the capacitor.
-
The – terminal is connected to a reference level, for example 0.25 x V
CC
.
-
The output filter should be used to minimize switching noise.
-
CAOUT used to gate Timer_A CCI1B, capturing capacitor discharge time.
More than one resistive element can be measured. Additional elements are
connected to CA0 with available I/O pins and switched to high impedance
when not being measured.
Содержание MSP430x4xx Family
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Страница 304: ...5 20 FLL Clock Module ...
Страница 340: ...7 8 Supply Voltage Supervisor ...
Страница 348: ...8 8 16 Bit Hardware Multiplier ...
Страница 372: ...9 24 32 Bit Hardware Multiplier ...
Страница 400: ...10 28 DMA Controller ...
Страница 428: ...13 10 Basic Timer1 ...
Страница 466: ...15 24 Timer_A ...
Страница 522: ...17 30 USART Peripheral Interface UART Mode ...
Страница 544: ...18 22 USART Peripheral Interface SPI Mode ...
Страница 672: ...23 12 Comparator_A ...
Страница 692: ...24 20 LCD Controller ...
Страница 746: ...26 28 ADC12 ...