C8051F91X-C8051F90X 查看數據表（PDF） - Silicon Laboratories
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C8051F91X-C8051F90X Datasheet PDF : 318 Pages
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C8051F91x-C8051F90x
7.6. Comparator0 and Comparator1 Analog Multiplexers
Comparator0 and Comparator1 on C8051F91x-C8051F90x devices have analog input multiplexers to
connect Port I/O pins and internal signals the comparator inputs; CP0+/CP0- are the positive and negative
input multiplexers for Comparator0 and CP1+/CP1- are the positive and negative input multiplexers for
Comparator1.
The comparator input multiplexers directly support capacitive touch switches. When the Capacitive Touch
Sense Compare input is selected on the positive or negative multiplexer, any Port I/O pin connected to the
other multiplexer can be directly connected to a capacitive touch switch with no additional external
components. The Capacitive Touch Sense Compare provides the appropriate reference level for detecting
when the capacitive touch switches have charged or discharged through the on-chip Rsense resistor. The
Comparator outputs can be routed to Timer2 or Timer3 for capturing sense capacitor’s charge and
discharge time. See Section “25. Timers” on page 270 for details. See Application Note AN338 for details
on Capacitive Touch Switch sensing.
Any of the following may be selected as comparator inputs: Port I/O pins, Capacitive Touch Sense
Compare, VDD/DC+ Supply Voltage, Regulated Digital Supply Voltage (Output of VREG0), the VBAT
Supply voltage or ground. The Comparator’s supply voltage divided by 2 is also available as an input; the
resistors used to divide the voltage only draw current when this setting is selected. The Comparator input
multiplexers are configured using the CPT0MX and CPT1MX registers described in SFR Definition 7.5 and
SFR Definition 7.6.
CPTnMX
P0.1
P0.3
P0.5
P0.7
P1.1
P1.3
P1.5
Capacitive
VDD/DC+ CPnOUT Touch
R
R
Sense
Compare
R (1/3 or 2/3) x VDD/DC+
CPn-
Input
MUX
CPnOUT
Rsense
Only enabled when
P0.0
P0.2
P0.4
P0.6
P1.0
P1.2
P1.4
P1.6
Capacitive Touch
Sense Compare is
selected on CPn+
Input MUX.
Capacitive
VDD/DC+ CPnOUT Touch
R
R
Sense
Compare
R (1/3 or 2/3) x VDD/DC+
CPnOUT
CPn+
Input
MUX
Rsense
Only enabled when
Capacitive Touch
Sense Compare is
selected on CPn-
Input MUX.
VDD/DC+
+
-
VDD/DC+
VDD/DC+
GND
R
½ x VDD/DC+
R
½ x VDD/DC+
R Digital Supply
VDD/DC+
R
VBAT
GND
Figure 7.4. CPn Multiplexer Block Diagram
Important Note About Comparator Input Configuration: Port pins selected as comparator inputs should
be configured as analog inputs, and should be skipped by the Digital Crossbar. To configure a Port pin for
analog input, set to 0 the corresponding bit in register PnMDIN and disable the digital driver (PnMDOUT =
0 and Port Latch = 1). To force the Crossbar to skip a Port pin, set to 1 the corresponding bit in register
PnSKIP. See Section “21. Port Input/Output” on page 205 for more Port I/O configuration details.
Rev. 1.0
95
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