Charge Time Measurement Unit (CTMU) and
CTMU Operation with Threshold Detect
HIGHLIGHTS
This section of the manual contains the following major topics:
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
Introduction ....................................................................................................................... 2
Register Maps................................................................................................................... 4
CTMU Operation............................................................................................................. 10
Calibrating the CTMU Module......................................................................................... 12
Measuring Capacitance with the CTMU.......................................................................... 24
Measuring Time with the CTMU Module......................................................................... 32
Generating Delays with the CTMU Module..................................................................... 36
Measuring Temperature with the CTMU ......................................................................... 39
Operation During Sleep/Idle Modes................................................................................ 44
Effects of a Reset on CTMU ........................................................................................... 45
Low-Power Applications for Devices with a CTMREQ Bit .............................................. 45
Electrical Specifications .................................................................................................. 45
Related Application Notes............................................................................................... 46
Revision History .............................................................................................................. 47
2011-2016 Microchip Technology Inc.
DS30009743B-page 1
dsPIC33/PIC24 Family Reference Manual
1.0
INTRODUCTION
The Charge Time Measurement Unit (CTMU) is a flexible analog module that has a configurable
current source with a digital circuit built around it. The CTMU can be used for differential time
measurement between pulse sources and can be used for generating an asynchronous pulse.
By working with other on-chip analog modules, the CTMU can be used for high-resolution time,
capacitance, resistance, inductance and temperature measurement. The CTMU can also generate output pulses with a specific time delay. These measurements can be used in applications
including capacitive touch, humidity sensing and measuring relative changes in capacitance. The
CTMU is ideal for interfacing with capacitive-based sensors.
The module includes the following key features:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
On-chip precision current source
Sixteen-edge input trigger sources
Selection of edge or level-sensitive inputs
Polarity control for each edge source
Control of edge sequence
Control of response to edges
High-precision time measurement
Time delay of external or internal signal asynchronous to system clock
Integrated temperature sensing diode
Control of current source during auto-sampling
Four current source ranges
Time measurement resolution of one nanosecond or less
CTMU operation in Sleep mode
Relative measurements using Analog-to-Digital Converter Threshold Detect
The CTMU works in conjunction with the A/D Converter for time or charge measurement. When
configured for time delay, the CTMU is connected to one of the analog comparators. The input
edge sources can be selected from up to sixteen sources for each edge. For device-specific
information on available input sources, refer to the appropriate device data sheet.
A block diagram of the CTMU in Measurement mode is shown in Figure 1-1 and in Time Generation
(TGEN) mode in Figure 1-2.
DS30009743B-page 2
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Figure 1-1:
CTMU Measurement Mode Block Diagram
EDGEN
EDG1POL
EDG1SEL<3:0>
IRNG<1:0>
Timer1
CMPx
OCx
CTEDGx
ICx
ITRIM<5:0>
Current
Source
0
EDG1STAT
CTTRIG
1
Edge
Detect
EDG1MOD
ADC Trigger
CTEDG1
Timer1
CMPx
OCx
CTEDGy
ICx
IDISSEN
0
EDG2STAT
1
Edge
Detect
EDG2MOD
EDG2SEL<3:0>
AVSS
EDG2POL
ADC
EDGEN
AVSS
Temperature
Diode
ADxCHS
AVSS
Note 1: Refer to the particular device data sheet for specific edge source types and assignments.
Figure 1-2:
CTMU Time Generation Block Diagram
EDG1POL
EDG1SEL<3:0>
IRNG<1:0>
Current
Source
ITRIM<5:0>
Timer1
CMPx
OCx
CTEDGx
ICx
CTPLS
CTEDG1
IDISSEN
Timer1
CMPx
OCx
CTEDGy
ICx
AVSS
Comparator
CxIN
EDG2SEL<3:0>
EDG2POL
CVREF
Note 1: Refer to the particular device data sheet for specific edge source types and assignments.
2011-2016 Microchip Technology Inc.
DS30009743B-page 3
REGISTER MAPS
Depending on the device variant, there are up to three control registers available for the CTMU: CMTUCON1H, CTMUCON1L and
CTMUCON2L.
The CTMUCON1H and CTMUCON1L registers (Register 2-1 and Register 2-2) contain control bits for configuring the CTMU module
edge source selection, edge source polarity selection, edge sequencing, ADC trigger, current source range and current source trim. The
CTMUCON2L register (Register 2-3) has bits for selecting the Current Source Reset, and analog circuit capacitor discharge and
enables.
A summary of the registers associated with the dsPIC33/PIC24 CTMU and CTMU Operation with Threshold Detect is provided in
Table 2-1.
Table 2-1:
File Name
CTMU Register Map
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Bit 7
Bit 6
Bit 4
Bit 3
Bit 2
CTMUCON1H EDG1MOD EDG1POL EDG1SEL3 EDG1SEL2 EDG1SEL1
EDG1SEL0 EDG2STAT EDG1STAT EDG2MOD
CTMUCON1L
CTMUEN
—
CTMUSIDL
TGEN
EDGEN
EDGSEQEN
IDISSEN
CTTRIG
ITRIM5
ITRIM4
ITRIM3
ITRIM2
ITRIM1
ITRIM0
CTMUCON2L
—
—
—
—
—
—
—
—
—
—
—
IRSTEN
—
DSCHS2
Legend:
— = unimplemented, read as ‘0’. Reset values are shown in hexadecimal.
EDG2POL
Bit 5
EDG2SEL3 EDG2SEL2 EDG2SEL1 EDG2SEL0
Bit 1
Bit 0
All
Resets
—
IRNGH
0000
IRNG1
IRNG0
0000
DSCHS1 DSCHS0
0000
2011-2016 Microchip Technology Inc.
dsPIC33/PIC24 Family Reference Manual
DS30009743B-page 4
2.0
CTMU and CTMU Operation with Threshold Detect
Register 2-1:
CTMUCON1H: CTMU Control Register 1 High
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
EDG1MOD
EDG1POL
EDG1SEL3
EDG1SEL2
EDG1SEL1
EDG1SEL0
EDG2STAT
EDG1STAT
bit 15
bit 8
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
U-0
R/W-0
EDG2MOD
EDG2POL
EDG2SEL3
EDG2SEL2
EDG2SEL1
EDG2SEL0
—
IRNGH
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
x = Bit is unknown
bit 15
EDG1MOD: Edge 1 Edge-Sensitive Select bit
1 = Input is edge-sensitive
0 = Input is level-sensitive
bit 14
EDG1POL: Edge 1 Polarity Select bit
1 = Edge 1 is programmed for a positive edge response
0 = Edge 1 is programmed for a negative edge response
bit 13-10
EDG1SEL<3:0>: Edge 1 Source Select bits
1111 = CMP C3OUT
1110 = CMP C2OUT
1101 = CMP C1OUT
1100 = IC3 interrupt
1011 = IC2 interrupt
1010 = IC1 interrupt
1001 = CTED8 pin
1000 = CTED7 pin(1)
0111 = CTED6 pin
0110 = CTED5 pin
0101 = CTED4 pin
0100 = CTED3 pin(1)
0011 = CTED1 pin
0010 = CTED2 pin
0001 = OC1
0000 = Timer1 match
bit 9
EDG2STAT: Edge 2 Status bit
Indicates the status of Edge 2 and can be written to control current source.
1 = Edge 2 has occurred
0 = Edge 2 has not occurred
bit 8
EDG1STAT: Edge 1 Status bit
Indicates the status of Edge 1 and can be written to control current source.
1 = Edge 1 has occurred
0 = Edge 1 has not occurred
bit 7
EDG2MOD: Edge 2 Edge-Sensitive Select bit
1 = Input is edge-sensitive
0 = Input is level-sensitive
bit 6
EDG2POL: Edge 2 Polarity Select bit
1 = Edge 2 is programmed for a positive edge response
0 = Edge 2 is programmed for a negative edge response
Note 1:
CTED3, CTED7, CTED10 and CTED11 are not available on 64-pin packages.
2011-2016 Microchip Technology Inc.
DS30009743B-page 5
dsPIC33/PIC24 Family Reference Manual
Register 2-1:
CTMUCON1H: CTMU Control Register 1 High (Continued)
bit 5-2
EDG2SEL<3:0>: Edge 2 Source Select bits
1111 = CMP C3OUT
1110 = CMP C2OUT
1101 = CMP C1OUT
1100 = Peripheral clock
1011 = IC3 interrupt
1010 = IC2 interrupt
1001 = IC1 interrupt
1000 = CTED13 pin
0111 = CTED12 pin
0110 = CTED11 pin(1)
0101 = CTED10 pin(1)
0100 = CTED9 pin
0011 = CTED1 pin
0010 = CTED2 pin
0001 = OC1
0000 = Timer1 match
bit 1
Unimplemented: Read as ‘0’
bit 0
IRNGH: High-Current Range Select bit
Current output is set by the IRNG<1:0> bits in the CTMUCON1L register.
1 = Uses the higher current ranges (550 µA-2.2 mA)
0 = Uses the lower current ranges (550 nA-50 µA)
Note 1:
CTED3, CTED7, CTED10 and CTED11 are not available on 64-pin packages.
DS30009743B-page 6
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Register 2-2:
CTMUCON1L: CTMU Control Register 1 Low
R/W-0
U-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
CTMUEN
—
CTMUSIDL
TGEN
EDGEN
EDGSEQEN
IDISSEN
CTTRIG
bit 15
bit 8
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
ITRIM5
ITRIM4
ITRIM3
ITRIM2
ITRIM1
ITRIM0
IRNG1(2)
IRNG0(2)
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
x = Bit is unknown
bit 15
CTMUEN: CTMU Enable bit
1 = Module is enabled
0 = Module is disabled
bit 14
Unimplemented: Read as ‘0’
bit 13
CTMUSIDL: CTMU Stop in Idle Mode bit
1 = Discontinues module operation when device enters Idle mode
0 = Continues module operation in Idle mode
bit 12
TGEN: Time Generation Enable bit
1 = Enables edge delay generation and routes the current source to the comparator pin
0 = Disables edge delay generation and routes the current source to the selected ADC input pin
bit 11
EDGEN: Edge Enable bit
1 = Edges are not blocked
0 = Edges are blocked
bit 10
EDGSEQEN: Edge Sequence Enable bit
1 = Edge 1 event must occur before Edge 2 event can occur
0 = No edge sequence is needed
bit 9
IDISSEN: Analog Current Source Control bit
1 = Analog current source output is grounded
0 = Analog current source output is not grounded
bit 8
CTTRIG: CTMU Trigger Control bit
1 = Trigger output is enabled
0 = Trigger output is disabled
Note 1:
2:
Step-size is device dependent. Refer to the device data sheet for values.
All ranges are not available on all devices. Refer to the particular device data sheet for specific range
availability.
2011-2016 Microchip Technology Inc.
DS30009743B-page 7
dsPIC33/PIC24 Family Reference Manual
Register 2-2:
CTMUCON1L: CTMU Control Register 1 Low (Continued)
bit 7-2
ITRIM<5:0>: Current Source Trim bits
011111 = Maximum positive change from nominal current (+ 62% nominal)(1)
011110
•
•
•
000001 = Minimum positive change from nominal current (+ 2% nominal)
000000 = Nominal current output specified by IRNG<1:0>
111111 = Minimum negative change from nominal current (– 2% nominal)
•
•
•
100010
100001 = Maximum negative change from nominal current (– 64% nominal)(1)
bit 1-0
IRNG<1:0>: Current Source Range Select bits(2)
If IRNGH = 0:
11 = 55 µA range
10 = 5.5 µA range
01 = 550 nA range
00 = 550 µA range
If IRNGH = 1:
11 = Reserved; do not use
10 = Reserved; do not use
01 = 2.2 mA range
00 = 550 µA range
Note 1:
2:
Step-size is device dependent. Refer to the device data sheet for values.
All ranges are not available on all devices. Refer to the particular device data sheet for specific range
availability.
DS30009743B-page 8
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Register 2-3:
CTMUCON2L: CTMU Control Register 2 Low
U-0
U-0
U-0
U-0
U-0
U-0
U-0
U-0
—
—
—
—
—
—
—
—
bit 15
bit 8
U-0
U-0
U-0
R/W-0
U-0
—
—
—
IRSTEN(1)
—
R/W-0
R/W-0
R/W-0
DSCHS2(1,2) DSCHS1(1,2) DSCHS0(1,2)
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
x = Bit is unknown
bit 15-5
Unimplemented: Read as ‘0’
bit 4
IRSTEN: CTMU Current Source Reset Enable bit(1)
1 = Signal selected by the DSCHS<2:0> bits or the IDISSEN control bit will reset CTMU edge detect logic
0 = CTMU edge detect logic must be reset by software
bit 3
Unimplemented: Read as ‘0’
bit 2-0
DSCHS<2:0>: Discharge Source Select bits(1,2)
111 = CLC2 out
110 = CLC1 out
101 = Disabled
100 = ADC end of conversion
011 = MCCP3 auxiliary output
010 = MCCP2 auxiliary output
001 = MCCP1 auxiliary output
000 = Disabled
Note 1:
2:
This feature is not available on all devices. Refer to the device data sheet for availability.
Discharge sources are device-dependent. Refer to the device data sheet for available sources.
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DS30009743B-page 9
dsPIC33/PIC24 Family Reference Manual
3.0
CTMU OPERATION
The CTMU works by using a fixed current source to charge a circuit. The type of circuit depends
on the type of measurement being made. In the case of charge capacitive measurement, the current is fixed and the amount of time the current is applied to the circuit is fixed. The voltage level
read by the ADC is then a measurement of the capacitance of the circuit. In the case of time
measurement, the current, as well as the capacitance of the circuit, is fixed. The voltage read by
the ADC is then representative of the amount of time elapsed from the time the current source
starts and stops charging the circuit.
If the CTMU is being used as a time delay, both capacitance and current source are fixed, as well
as the reference voltage supplied to the comparator circuit. The delay of a signal is determined
by the amount of time it takes to charge the circuit to the comparator threshold voltage.
3.1
Theory of Operation
The operation of the CTMU is based on the equation for charge, as shown in Equation 3-1.
Equation 3-1:
dV
I = C ------dT
More simply, the amount of charge measured in coulombs in a circuit is defined as current in
amperes (I) multiplied by the amount of time in seconds that the current flows (t). Charge is also
defined as the capacitance in farads (C) multiplied by the voltage of the circuit (V), as shown in
Equation 3-2.
Equation 3-2:
It = CV
The CTMU module provides a constant, known current source. The A/D Converter is used to
measure (V) in the equation, leaving two unknowns: capacitance (C) and time (t). Equation 3-2
can be used to calculate capacitance or time, by either the relationship shown in Equation 3-3
and using the known fixed capacitance of the circuit, or by Equation 3-4 using a fixed time that
the current source is applied to the circuit.
Equation 3-3:
C V
t = ----------------I
Equation 3-4:
I t
C = ------------V
DS30009743B-page 10
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
3.2
Current Source
At the heart of the CTMU is a precision calibratable current source, designed to provide a constant
reference for measurements. The amount of current is user-selectable across four ranges, or a total
of three orders of magnitude, with the ability to trim the output in ±2% increments (nominal). The
current range is selected by the IRNG<1:0> bits (CTMUCON1L<1:0>).
Current trim is provided by the 2’s complement signed ITRIM<5:0> bits (CTMUCON1L<7:2>).
These six bits allow trimming of the current source in steps of approximately 2% per step. A value
of ‘000000’ is the middle value (no change). A value of ‘100000’ is the maximum negative
adjustment (approximately -64%) and ‘011111’ is the maximum positive adjustment
(approximately +62%).
3.3
Edge/Level Selection and Control
CTMU measurements are controlled by the edge or level events occurring on the module’s two
input channels. Each channel, referred to as Edge 1 and Edge 2, can be configured to receive input
pulses from one of the sixteen edge input pins. The inputs are selected using the EDG1SEL<3:0>
and EDG2SEL<3:0> bit pairs (CTMUCON1H<13:10> and <5:2>). Further, the mode of the input
sources to the Edge 1 and Edge 2 can either be level-sensitive or edge-sensitive, which is selected
using the EDG1MOD bit (CTMUCON1H<15>).
In addition to source, each channel can be configured for event polarity using the EDG1POL and
EDG2POL bits (CTMUCON1H<14,6>). The input channels can also be filtered for an edge
event sequence (Edge 1 occurring before Edge 2) by setting the EDGSEQEN bit
(CTMUCON1L<10>).
3.4
Edge Status
The CTMUCON1H register also contains two status bits: EDG2STAT and EDG1STAT
(CTMUCON1H<9:8>). Their primary function is to show if an edge response has occurred on the
corresponding channel. The CTMU automatically sets a particular bit when an edge response is
detected on its channel. The level-sensitive, or edge-sensitive, nature of the input channels also
means that the status bits become set immediately if the channel’s configuration is changed and
is the same as the channel’s current state.
The module uses the edge status bits to control the current source output to external analog
modules (such as the A/D Converter). Current is only supplied to external modules when
EDG1STAT is not equal to EDG2STAT and shuts current off when EDG1STAT is equal to
EDG2STAT. This allows the CTMU to measure current only during the interval between edges.
After both status bits are set, it is necessary to clear them before another measurement is taken.
Both bits should be cleared simultaneously to avoid re-enabling the CTMU current source.
In addition to being set by the CTMU hardware, the edge status bits can also be set by software.
This allows the user’s application to manually enable or disable the current source. Setting either
one (but not both) of the bits enables the current source. Setting or clearing both bits at once
disables the source.
3.5
Interrupts
The CTMU sets its interrupt flag whenever the current source is enabled and disabled. The
CTMU interrupt enable bit must also be set to generate interrupts. If edge sequencing is not
enabled, Edge 1 must occur before Edge 2 to generate an interrupt. If edge sequencing is not
enabled, it is necessary to monitor the edge status bits and determine which edge occurred last
and caused the interrupt.
2011-2016 Microchip Technology Inc.
DS30009743B-page 11
dsPIC33/PIC24 Family Reference Manual
4.0
CALIBRATING THE CTMU MODULE
The CTMU requires calibration for precise measurements of capacitance and time, as well as for
generating an accurate time delay. If the application only requires measurement of a relative
change in resistance, capacitance or time, calibration is usually not necessary. These applications include capacitive touch switching, in which the touch circuit has a baseline capacitance
and the added capacitance of the human body changes the overall capacitance of a circuit. If
actual resistance, capacitance or time measurement is required, calibration is required.
4.1
Current Source Calibration
This calibration consists of measuring the CTMU current source generated voltage drop across
a known value resistor (RCAL) using the ADC. The CTMU trim is adjusted until the ADC
measured value is within the desired tolerance. The value for RCAL depends on the current
source range (refer to Table 4-1 for suggested RCAL values). The RCAL value can be also be calculated using Equation 4-1. After the RCAL value has been determined, the expected ADC counts
can be calculated using Equation 4-2. An example calculation is provided in Example 4-1.
There are two current calibrations; the appropriate one depends on the current range used in the
application. For current source ranges of 550 µA or 5.5 µA, the Low-Current mode calibration is
appropriate; it can typically be performed on any analog input pin. For the higher CTMU ranges,
the internal resistances have a significant effect on the calibration, therefore, the High-Current
mode calibration is appropriate. The High-Current mode calibration is typically limited to a single
device pin with a dedicated connection to the CTMU (refer to the specific device data sheet for
more information).
Equation 4-1:
Current Source RCAL Value Calculation
RCAL =
Note 1:
ADCVREF * 70%(1)
CTMU Range
Refer to Section 4.3 “Calibration and Measurement Considerations”.
Equation 4-2:
Current Source Expected ADC Counts Calibration
Expected Counts =
Example 4-1:
RCAL * CTMU Range * (2^ADC Bits)
ADCVREF
Current Source Calibration
ADCVREF = 3.3V, 10-Bit ADC Mode, CTMU Range is 0.550 µA:
RCAL =
3.3V * 70%
0.550 µA
Expected Counts =
DS30009743B-page 12
= 4.22 MOhms Common 1% Resistor 4.22 MOhms
4.22 MOhms * 0.550 µA * 1023
3.3V
= 720 Counts
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
4.1.1
LOW-CURRENT RANGE MODE CALIBRATION
This calibration is only suitable for the 550 µA and 5.5 µA ranges. The large ratio of RCAL to RESD
and RMUX allows the RESD and RMUX values to be ignored to simplify the calculations (refer to
Figure 4-1). The calibration process consists of enabling the current source and sampling the
voltage generated across RCAL. This voltage is then divided by the known resistor value to calculate the CTMU current. The trim is then iteratively adjusted until the desired calibration is
achieved. To configure the device for current calibration, perform the following steps (refer to
Example 4-2).
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Configure the CTMU for current generation (TGEN = 0).
Configure the I/O port pin as an input and enable Analog mode.
Configure the ADC for Manual mode.
Enable the CTMU.
Enable the current source by setting the EDG1STAT bit.
Start sampling.
Wait approximately 1500 µs for the sample capacitor to charge.
Convert the analog sample.
Disable the CTMU.
Repeat ‘n’ times, accumulating the values and averaging the result.
Calculate the current.
Iteratively adjust the trim value until the result is the desired CTMU current.
Figure 4-1:
Low-Current Range Mode Calibration Block Diagram
AVDD
EDG1
EDG2
ena
ANx
RESD
RCAL
ADC
RMUX
ADxCHS
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DS30009743B-page 13
dsPIC33/PIC24 Family Reference Manual
Example 4-2:
#include
#define
#define
#define
#define
#define
Low-Current Range Mode Calibration
"p24FJ1024GB610.h"
CTMU_MODE_EDGE 0
RANGE_0_550uA 1
RCAL 4.22e6
ADSCALE 1023
ADREF 3.3
// .550uA
// R value is 4.22M
//for 10-bit ADC
//Vdd connected to ADC Vref+
unsigned
int CtmuCurrentCalConfig(unsigned int mode, unsigned int range, signed int trim)
{
unsigned
int result, x;
// Step 1 Configure the CTMU
CTMUCON1L = 0x0000;
// Disable CTMU
CTMUCON1Lbits.TGEN = mode;
// Enable/Disable Time Generation mode
CTMUCON1Lbits.EDGEN = 0;
// Edges are disabled
CTMUCON1Lbits.IDISSEN = 0;
// Current source is not grounded
CTMUCON1Lbits.ITRIM = trim;
// Set trim
CTMUCON1Lbits.CTTRIG = 0;
// Trigger output disabled
CTMUCON1Lbits.IRNG = (range & 3);
// Set range
CTMUCON1H = 0;
// Edges are disabled, edge controls ignored
// Next line does not apply to all devices
CTMUCON1Hbits.IRNGH = (range>>2);
// set high bit of range
CTMUCON2Lbits.IRSTEN = 0;
// Current source reset disabled
CTMUCON2Lbits.DSCHS = 0;
// Discharge source disabled
// Step 2 Configure the GPIO Port
TRISB = TRISB | (1<<2);
ANSBbits.ANSB2 = 1;
// Set channel 2
// Make AN2 as analog (Resistor is connected to this pin)
// Step 3 configure the ADC
AD1CHSbits.CH0SA = 2;
// Select the analog channel 2
AD1CON1 = 0x8000;
// Turn On A/D Converter,
// Unsigned fractional format, Clear SAMP bit to
// start conversion, Sample when SAMP bit is set
AD1CON2 = 0x0000;
// VR+ = AVDD, V- = AVSS, Don't scan,
AD1CON3 = 0x0000;
// ADC uses system clock
AD1CON3bits.ADCS = 0;
// conversion clock = 1xTcy
AD1CON5 = 0x0000;
// Auto-Scan disabled
// Step 4 - 6 Enable the current source and start sampling
CTMUCON1Lbits.CTMUEN = 1;
// Enable the CTMU
CTMUCON1Hbits.EDG1STAT = 1;
// Enable current source
AD1CON1bits.SAMP = 1;
// Manual sampling start
// step 7 ~3000 us delay to charge sample cap
for (x = 0; x < 2000; x++);
// ~6 cycles * 2000 ,Fcy = 4Mhz
// step 8 Convert the sample
AD1CON1bits.SAMP = 0;
while(AD1CON1bits.DONE == 0);
// Step 9 Disable the CTMU
CTMUCON1Hbits.EDG1STAT = 0;
IFS0bits.AD1IF = 0;
CTMUCON1Lbits.CTMUEN = 0;
result = ADC1BUF0;
return (result);
// Begin A/D conversion
// Wait for A/D convert complete
// Disable current source
// Clear ADC interrupt flag
// Disable the CTMU
// return accumulated result
}
DS30009743B-page 14
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Example 4-2:
Low-Current Range Mode Calibration (Continued)
#define
ITT 10
int
{
main(void)
// 10 iterations
float cntsAvg, vCal, cntsTot = 0, ctmuISrc = 0, result = 0;
// Step 10 perform calibration 10 times
for(x = 0; x < ITT; x++)
{
result = (float)(CtmuCurrentCalConfig(CTMU_MODE_EDGE, RANGE_0_550uA, 0)); // 0.550uA , no trim
cntsTot += (float)result;
}
// Step 11 calculate the result
cntsAvg = (cntsTot / ITT);
vCal = (cntsAvg / ADSCALE * ADREF);
ctmuISrc = vCal / RCAL;
// Average of 10 readings
// CTMU current in uA
// step 12
// user code to perform iteration for calibration
while(1);
}
2011-2016 Microchip Technology Inc.
DS30009743B-page 15
dsPIC33/PIC24 Family Reference Manual
4.1.2
HIGH-CURRENT MODE CALIBRATION
High-Current mode calibration uses a dedicated connection to a special device pin to remove the
RMUX voltage offset seen in the Low-Current mode calibration method. These offsets become a
significant source of error for the higher current ranges. While this method is intended for the
high-current ranges, it can be used to improve the calibration accuracy on the low-current
ranges. This method typically achieves a calibration tolerance of less than 3% on all ranges (refer
to Figure 4-2). The calibration process consists of enabling the current source and sampling the
voltage generated across RCAL. This voltage is then divided by the known resistor value to calculate the CTMU current. The trim is then iteratively adjusted until the desired calibration is
achieved. To configure the device for current calibration, perform the following steps (refer to
Example 4-3).
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Configure the CTMU for Time Generation mode (TGEN = 1).
Configure the I/O port pin as an input and enable Analog mode.
Configure the ADC for Manual mode.
Enable the CTMU.
Enable the current source by setting the EDG1STAT bit.
Start sampling.
Wait approximately 1500 µs for the sample capacitor to charge.
Convert the analog sample.
Disable the CTMU.
Repeat ‘n’ times, accumulating the values and averaging the result.
Calculate the current.
Iteratively adjust the trim value until the result is the desired CTMU current.
Refer to Example 4-3 and Equation 4-1.
Figure 4-2:
High-Current Range Mode Calibration Block Diagram
RESD
ADC
RMUX
ADXCHS
AVDD
EDG1
EDG2
ena
TGEN
C2INB
RESD
REXT
AVSS
DS30009743B-page 16
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Example 4-3:
#include
#define
#define
#define
#define
#define
High-Current Range Mode Calibration
"p24FJ1024GB610.h"
_MODE_TGEN 1
RANGE_550uA
0
RCAL 4.22e6
ADSCALE 1023
ADREF 3.3
// 550uA
// R value is 4200000 (4.22M)
//for 10-bit ADC
//Vdd connected to ADC Vr+
unsigned
int CtmuCurrentCalConfig(unsigned int mode, unsigned int range, signed int trim)
{
unsigned int
result, x;
// Step 1 Configure the CTMU
CTMUCON1L = 0x0000;
// Disable CTMU
CTMUCON1Lbits.TGEN = mode;
// Enable/Disable Time Generation mode
CTMUCON1Lbits.EDGEN = 0;
// Edges are disabled
CTMUCON1Lbits.IDISSEN = 0;
// Current source is not grounded
CTMUCON1Lbits.ITRIM = trim;
// Set trim
CTMUCON1Lbits.CTTRIG = 0;
// Trigger output disabled
CTMUCON1Lbits.IRNG = (range & 3);
// Set range
CTMUCON1H = 0;
// Edges are disabled, edge controls ignored
// Next line does not apply to all devices
CTMUCON1Hbits.IRNGH = (range>>2);
// set high bit of range
CTMUCON2Lbits.IRSTEN = 0;
CTMUCON2Lbits.DSCHS = 0;
// Current source reset disabled
// Discharge source disabled
// Step 2 Configure the GPIO Port
TRISB = TRISB | (1<<2);
ANSBbits.ANSB14 = 1;
// Set channel 2
// Make AN2 as analog (Resistor is connected to this pin)
// Step 3 configure the ADC
AD1CHSbits.CH0SA = 2;
// Select the analog channel(2)
AD1CON1 = 0x8000;
// Turn On A/D Converter,
// Unsigned fractional format, Clear SAMP bit to
// start conversion, Sample when SAMP bit is set
AD1CON2 = 0x0000;
// VR+ = AVDD, V- = AVSS, Don't scan,
AD1CON3 = 0x0000;
// ADC uses system clock
AD1CON3bits.ADCS = 0;
// conversion clock = 1xTcy
AD1CON5 = 0x0000;
// Auto-Scan disabled
// Step 4 - 6 Enable the current source and start sampling
CTMUCON1Lbits.CTMUEN = 1;
// Enable the CTMU
CTMUCON1Hbits.EDG1STAT = 1;
// Enable current source
AD1CON1bits.SAMP = 1;
// Manual sampling start
/// step 7 ~3000 us delay to charge sample cap
for (x = 0; x < 2000; x++);
// ~6 cycles * 2000 ,Fcy = 4Mhz
// step 8 Convert the sample
AD1CON1bits.SAMP = 0;
while(AD1CON1bits.DONE == 0);
// Step 9 Disable the CTMU
CTMUCON1Hbits.EDG1STAT = 0;
IFS0bits.AD1IF = 0;
CTMUCON1Lbits.CTMUEN = 0;
result = ADC1BUF0;
return (result);
// Begin A/D conversion
// Wait for A/D convert complete
// Disable current source
// Clear ADC interrupt flag
// Disable the CTMU
// return accumulated result
}
2011-2016 Microchip Technology Inc.
DS30009743B-page 17
dsPIC33/PIC24 Family Reference Manual
Example 4-3:
High-Current Range Mode Calibration (Continued)
#define ITT 10
int
{
// 10 iterations
main(void)
float cntsAvg, vCal, cntsTot = 0, ctmuISrc = 0, result;
// Step 10 perform calibration 10 times
for(x = 0; x < ITT; x++)
{
result = (float)(CtmuCurrentCalConfig(_MODE_TGEN, RANGE_550uA, 0));
cntsTot += result;
}
// Step 11 calculate the result
cntsAvg = (cntsTot / ITT);
vCal = (cntsAvg / ADSCALE * ADREF);
ctmuISrc = vCal / RCAL;
// 550uA, no trim
// Average of 10 readings
// CTMU current in uA
// step 12
// user code to perform iteration for calibration
while(1);
}
Table 4-1:
DS30009743B-page 18
Suggested Calibration (RCAL) Values
Range
RCAL Value (Ohms)
0.550 µA
4.22 MOhms
5.5 µA
422 kOhms
55 µA
42.2 kOhms
550 µA
4.2 kOhms
2.2 mA
1 kOhms
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
4.2
Capacitance Calibration
The capacitance calibration consists of measuring the system capacitance without the load to be
measured. The capacitance is calculated using the charge time, current and resulting voltage;
where current is known from the current source measurement step, t is a known fixed delay and
V is measured by performing an ADC conversion. This measured value, the offset, can then be
stored and subtracted from calculations of time measurement or capacitance measurement. For
calibration, the time delay can be approximated if the approximate values of CSTRAY and CADC
are known (refer to Equation 4-3 and Equation 4-4). Please refer to the respective device data
sheet for the value of CADC.
For capacitance calibration, the current source is first calibrated using a procedure from Section 4.1
“Current Source Calibration”. The calibration resistor is then removed or another analog channel
is used for the capacitance calibration. The calibrated current source is then enabled, while the ADC
is sampling, to charge the ADC sample capacitor and the system capacitance. The ADC conversion
is started after a precise delay. The ADC conversion result and the delay period are then used to
calculate the system capacitance (refer to Equation 4-5 and Example 4-4). This value can then be
subtracted from future measurements to account for the system capacitance. To minimize the effect
of noise and use the linear operating range of the current source, the delay period should be chosen
or adjusted such that the measured voltage is approximately 70% of AVDD. Refer to Section 4.3
“Calibration and Measurement Considerations”.
Equation 4-3:
Delay Time Calculation
Time =
Equation 4-4:
CTOTAL * VDESIRED
I
Delay Calculation with Known CSTRAY and CADC Values
(4 pF + 11 pF) * 2.31V/0.55 µA = 63 µs Delay
Equation 4-5:
System Capacitance Calculations
COFFSET = CSYSTEM = CADC + CSTRAY = (I * t)/V
Example 4-4:
Calculating the System Capacitance
Delay = 2.25 ms
CTMU Range = 0.55 µA
ADC Sample = 670 Counts (cnts) (ADC in 10-bit mode)
ADC Reference Voltage = 3.3V
Using Equation 4-5:
C=
2011-2016 Microchip Technology Inc.
0.55 µA * 2.25 ms
Current * Delay
=
= 573 pF
3.3V * (670 cnts/1023 cnts)
Voltage
DS30009743B-page 19
dsPIC33/PIC24 Family Reference Manual
Figure 4-3:
Capacitance Calibration Block Diagram
AVDD
EDG1
EDG2
ena
ANx
RESD
ADC
RMUX
ADxCHS
Capacitance calibration can be performed using the configuration from the Current mode calibration with the RCAL resistor disconnected or using a different pin for calibrations and measurements.
To configure the device for capacitance calibration, perform the following steps:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
DS30009743B-page 20
Perform current calibration (refer to Section 4.1 “Current Source Calibration”).
Configure the CTMU for current generation (TGEN = 0).
Configure the I/O port pin as an input and enable Analog mode.
Configure the ADC for Manual mode.
Enable the CTMU.
Enable the current source by setting the EDG1STAT bit.
Start sampling.
Discharge the internal charge by shorting the current source to ground.
Delay approximately 1200 µs to allow the internal circuit to discharge.
Disconnect the current source from ground.
Wait a predetermined time for the sample capacitor to charge.
Convert the analog sample.
Disable the CTMU.
Repeat 10 times, accumulating the values and averaging the result.
Calculate the capacitance using Equation 4-2.
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Example 4-5:
#include
#define
#define
#define
#define
#define
Absolute Capacitance Calibration and Measurement
"p24FJ1024GB610.h"
CTMU_MODE_EDGE 0
RANGE_0_550uA 1
ADSCALE 1023
ADREF 3.3
DELAY_LOOPS 150
// .550uA
//for 10-bit ADC
//Vdd connected to ADC Vr+
// delay = 6 cycles * DELAY_LOOPS * (1/4 MHz)
Fosc = 8MHz
unsigned
int CtmuCapMeasureConfig(unsigned int mode, unsigned int range, signed int trim)
{
unsigned int result, x;
// Step 1 Configure the CTMU
CTMUCON1L = 0x0000;
// Disable CTMU
CTMUCON1Lbits.TGEN = mode;
// Enable/Disable Time Generation mode
CTMUCON1Lbits.EDGEN = 0;
// Edges are disabled
CTMUCON1Lbits.IDISSEN = 1;
// Current source is grounded (discharge enabled)
CTMUCON1Lbits.ITRIM = trim;
// Set trim
CTMUCON1Lbits.CTTRIG = 0;
// Trigger output disabled
CTMUCON1Lbits.IRNG = (range & 3);
// Set range
CTMUCON1H = 0;
// Edges are disabled, edge controls ignored
// Next line does not apply to all devices
CTMUCON1Hbits.IRNGH = (range>>2);
// set high bit of range
CTMUCON2Lbits.IRSTEN = 0;
CTMUCON2Lbits.DSCHS = 1;
// Current source reset disabled
// Discharge source enabled
// Step 2 Configure the port Ports
TRISB = TRISB | (1<<2);
ANSBbits.ANSB14 = 1;
// Set channel 2
// Make AN2 as analog
// Step 3 configure the ADC
AD1CHSbits.CH0SA = 2;
AD1CON1 = 0x8000;
// Turn On A/D Converter,
// Unsigned fractional format, Clear SAMP bit to
// start conversion, Sample when SAMP bit is set
AD1CON2 = 0x0000;
// VR+ = AVDD, V- = AVSS, Don't scan,
AD1CON3 = 0x0000;
// ADC uses system clock
AD1CON3bits.ADCS = 0;
// conversion clock = 1xTcy
AD1CON5 = 0x0000;
// Auto-Scan disabled
// Step 4 - 6 Enable the current source and start sampling
CTMUCON1Lbits.CTMUEN = 1;
// Enable the CTMU
CTMUCON1Hbits.EDG1STAT = 1;
// Enable current source
AD1CON1bits.SAMP = 1;
// Manual sampling start
// step 7 1500us delay to discharge sample cap
for (x = 0; x < 5000; x++);
// ~6 cycles * 5000
// step 9 disable discharge
CTMUCON1Lbits.IDISSEN = 0;
// Discharge disabled
// step 10 delay to charge sample cap
for (x = 0; x < DELAY_LOOPS; x++);
// 6 clocks per loop iteration
// step 11 convert the sample
AD1CON1bits.SAMP = 0;
while(AD1CON1bits.DONE == 0);
2011-2016 Microchip Technology Inc.
// Begin A/D conversion
// Wait for A/D convert complete
DS30009743B-page 21
dsPIC33/PIC24 Family Reference Manual
Example 4-5:
Absolute Capacitance Calibration and Measurement (Continued)
// Step 12 disable the CTMU
CTMUCON1Hbits.EDG1STAT = 0;
IFS0bits.AD1IF = 0;
CTMUCON1Lbits.CTMUEN = 0;
result = ADC1BUF0;
// Disable current source
// Clear ADC interrupt flag
// Disable the CTMU
return (result);
// return accumulated result
}
#define ITT 10
int
{
// 10 iterations
main(void)
float cntsAvg, cntsTot = 0, c;
unsigned int x;
// Step 10 perform measurement 10 times
for(x = 0; x < ITT; x++)
{
cntsTot += (float)(CtmuCapMeasureConfig(CTMU_MODE_EDGE, RANGE_0_550uA, 0));
}
// Step 11 calculate the result
cntsAvg = (cntsTot / ITT);
// Average of 10 readings
c = (.550e-6 * DELAY_LOOPS * 6 * (1 / 4e6)) / (3.3 * cntsAvg / ADSCALE);
// step 12
// user code to perform iteration for calibration
// .550uA, no trim
// capacitance in Farads
while(1);
}
DS30009743B-page 22
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
4.3
Calibration and Measurement Considerations
The following should be considered when performing calibrations:
1.
2.
3.
4.4
The actual value of the calibration resistor is not important, but it should meet the following
requirements:
• The generated voltage across the resistor should be between ½ and ¾ of the ADC
full-scale value to minimize the noise effect on the measurement, and to stay in the
linear range of the current source. The current source operates in a linear fashion
when the developed load voltage is less than (AVDD – 0.7V, typical).
• The tolerance of the resistor is not important if the actual value of the resistor is known
and that value is used in the calculations.
• The chosen resistor value should be at least 100 times the internal resistance to
minimize the offsets generated by the internal resistors.
• For capacitance calibrations, the delay time should be chosen such that the ADC
sample capacitor charges to between ½ and ¾ of the ADC range to maximize
resolution and reduce the impact of noise.
The delay time for the current calibration should be sufficient to allow the ADC sample
capacitor to charge to a steady-state value.
Measurement resolution may be increased by using an external ADC reference that is
approximately ¾ of AVDD.
Measuring Internal Resistance
The value of the internal resistances can be measured and used in calculations to improve the
accuracy of calibrations and current measurements. The current source must first be calibrated.
The device is then configured for current measurement, but the I/O pin is driven low. When the
measurement is taken, the measured voltage is the drop across the internal resistance. This
value can then be subtracted from future measurements to improve accuracy.
2011-2016 Microchip Technology Inc.
DS30009743B-page 23
dsPIC33/PIC24 Family Reference Manual
5.0
MEASURING CAPACITANCE WITH THE CTMU
There are two methods of measuring capacitance with the CTMU. The first is the absolute
method, in which the actual capacitance value is desired. The second is the relative method, in
which the actual capacitance value is not required, rather a detection of change in capacitance
is desired.
5.1
Absolute Capacitance Measurement
For absolute capacitance measurements, both the current and capacitance calibration steps found
in Section 4.0 “Calibrating the CTMU Module” should be followed. The process for absolute
measurement is the same as the capacitance calibration process, but the load to be measured is
connected during measurement. The capacitance value from the calibration step is then subtracted
from the measured result to get the capacitance value. Refer to Example 4-5 for example code. If
the capacitance to be measured is significantly larger than the system capacitance measured in the
calibration step, the delay to charge the sample capacitor may have to be adjusted to allow the
capacitor to charge to a measurable value or to provide the desired resolution in the result. The
selected delay should not allow the resulting voltage to exceed 75% of the ADC reference voltage
(refer to Section 4.3 “Calibration and Measurement Considerations”).
Figure 5-1:
Capacitance Measurement Block Diagram
AVDD
EDG1
EDG2
ena
ANx
RESD
ADC
RMUX
ADxCHS
DS30009743B-page 24
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
5.2
Relative Charge Measurement and Capacitive Touch Sense
Relative measurements may not require precise capacitance measurements. For example, when
detecting a valid press of a capacitance-based switch, detecting a relative change of capacitance
is of interest. In this type of application, when the button is not touched, the total capacitance is system capacitance (the PCB traces, the ADC, etc.). A larger voltage will be measured by the ADC
due to the relatively smaller capacitance. When the button is pressed, the total capacitance is larger
due to the addition of the capacitance of the human body to the above listed capacitances, and a
smaller voltage will be measured by the ADC. Software then compares the non-touched values to
the current ADC result to determine if a button has been touched. The threshold values used to
determine a touch event are dependent on the system and the environment, and therefore, should
be determined experimentally. Typical implementations do not require calibration to operate. ESD
protection must be provided on capacitive touch pins (refer to Section 5.4 “Electrostatic
Discharge (ESD) Protection”).
Detecting capacitance changes is accomplished with the following steps:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
Configure the CTMU for current generation (TGEN = 0).
Configure the I/O port pin as an input and enable Analog mode.
Configure the ADC for Manual mode.
Enable the CTMU.
Enable the current source by setting the EDG1STAT bit.
Start sampling.
Enable discharge circuit.
Delay to allow the internal circuit to discharge.
Disable the discharge circuit.
Wait a predetermined time for the sample capacitor to charge (delay).
Convert the analog sample.
Disable the current source.
Calculate the total capacitance using Equation 4-5. Refer to Example 5-1.
Subtract the system capacitance from the result (optional).
Compare the result to the system capacitance.
Repeat Steps 5-15 if averaging is required.
Figure 5-2:
Capacitance Touch Measurement Block Diagram
AVDD
EDG1
EDG2
ena
ANx
RESD
Touch Pad
ADC
RMUX
ADxCHS
2011-2016 Microchip Technology Inc.
DS30009743B-page 25
dsPIC33/PIC24 Family Reference Manual
Example 5-1:
#include
#define
#define
#define
Capacitance Touch
"p24FJ1024GB610.h"
CTMU_MODE_EDGE 0
RANGE_0_550uA 1
// .550uA
CTMU_TOUCH_THRESHHOLD_OFFSET 100
void
CtmuCapTouchConfig(unsigned int mode, unsigned int range, signed int trim)
{
// step 1 Configure the CTMU
CTMUCON1L = 0x0000;
// Disable CTMU
CTMUCON1Lbits.TGEN = mode;
// Enable/Disable Time Generation mode
CTMUCON1Lbits.EDGEN = 0;
// Edges are disabled
CTMUCON1Lbits.ITRIM = trim;
// Set trim
CTMUCON1Lbits.CTTRIG = 0;
// Trigger output disabled
CTMUCON1Lbits.IRNG = (range & 3);
// Set range
CTMUCON1H = 0;
// Edges are disabled, edge controls ignored
// This line does not apply to all devices
CTMUCON1Hbits.IRNGH = (range>>2);
// set high bit of range
CTMUCON2Lbits.IRSTEN = 0;
CTMUCON2Lbits.DSCHS = 0;
// Current source reset disabled
// Discharge source disabled
// Step 2 Configure the port Ports
TRISB = TRISB | (1<<2);
ANSBbits.ANSB2 = 1;
// Set channel 2
// Make AN2 as analog
// Step 3 configure the ADC
AD1CHSbits.CH0SA = 2;
// Select the analog channel(2)
AD1CON1 = 0x8000;
// Turn On A/D Converter,
// Unsigned fractional format, Clear SAMP bit to
// start conversion, Sample when SAMP bit is set
AD1CON2 = 0x0000;
// VR+ = AVDD, V- = AVSS, Don't scan,
AD1CON3 = 0x0000;
// ADC uses system clock
AD1CON3bits.ADCS = 0;
// conversion clock = 1xTcy
AD1CON5 = 0x0000;
// Auto-Scan disabled
}
unsigned
int
CtmuReturnSample(void)
{
unsigned
int
result, x;
// Step 4 - 7 Enable the current source and start sampling
CTMUCON1Lbits.CTMUEN = 1;
// Enable the CTMU
CTMUCON1Hbits.EDG1STAT = 1;
// Enable current source
CTMUCON1Lbits.IDISSEN = 1;
// Enable discharge
AD1CON1bits.SAMP = 1;
// Manual sampling start
// step 8 1500us delay to discharge sample cap
for (x = 0; x < 2000; x++);
// ~6 cycles * 2000
// step 9 Disable the discharge circuit
CTMUCON1Lbits.IDISSEN = 0;
// Disable discharge (start charging)
// step 10 allow the sample cap to partially charge
for (x = 0; x < 250; x++);
// ~6 cycles * 250 ~ 670 cnts
// step 11 Convert the analog sample
AD1CON1bits.SAMP = 0;
// Begin A/D conversion
while(AD1CON1bits.DONE == 0);
// Wait for A/D convert complete
DS30009743B-page 26
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Example 5-1:
Capacitance Touch (Continued)
// Step 12 Disable the current source
CTMUCON1Hbits.EDG1STAT = 0;
// Disable current source
IFS0bits.AD1IF = 0;
// Clear ADC interrupt flag
CTMUCON1Lbits.CTMUEN = 0;
// Disable the CTMU
result = ADC1BUF0;
return (result);
}
int
{
main(void)
unsigned
int
untouched, sample;
CtmuCapTouchConfig(CTMU_MODE_EDGE, RANGE_0_550uA, 0);
untouched = CtmuReturnSample();
// get reference value
while(1)
{
sample = CtmuReturnSample();
// step 14-15 subtract the threshold and test
if (sample < untouched - CTMU_TOUCH_THRESHHOLD_OFFSET)
{
// button was pressed
}
// user code
}
}
2011-2016 Microchip Technology Inc.
DS30009743B-page 27
dsPIC33/PIC24 Family Reference Manual
5.3
Capacitance Touch Sense with Auto-Threshold Detect ADCs
The CTMU, when combined with a trigger source and an ADC with Auto-Threshold Detect, form a
semi-autonomous relative charge detect sub-system that can be used for capacitive touch sense.
The trigger source, such as an OCMP module, enables the CTMU current source for a predetermined period, charging the capacitor. The resulting voltage is determined by the capacitance of the
system and additional capacitance of a touch. The ADC is configured to automatically convert a list
of channels corresponding to the touch sensors. The Threshold Detect is configured with a
predefined level, and therefore, the ADC only generates an interrupt when that threshold is met (a
button is touched). See Figure 5-2. Figure 5-3 illustrates the timing relationships for 2 scanned
channels. The ADC interrupt occurs after the lower voltage is detected on Channel 2. User code
then clears the ADC interrupt. User code must also clear the timer interrupt. Calibration is not
typically required with relative sense applications. ESD protection must be provided on capacitive
touch pins (refer to Section 5.4 “Electrostatic Discharge (ESD) Protection”).
1.
2.
3.
4.
5.
6.
7.
8.
Figure 5-3:
Configure the GPIO ports.
Configure the CTMU for External Edge Trigger Reset and ADC control of discharge.
Configure the ADC for Threshold Detect and auto-scan.
Configure a scan trigger (Timer1).
Wait for an interrupt (this can be implemented as an ISR).
Clear the interrupt flag.
Determine the channel that caused the interrupt.
Clear the appropriate Channel Hit flag.
Capacitance Touch Sense with Auto-Threshold Detect ADCs Timing Diagram
Auto-Scan Channels
AN1
Discharge
Charge
AN2
Convert
Discharge
Charge
Convert
ASENA
AN0 Voltage
AN1 Voltage
No Touch
Event
Touch
Event
TMR1IF
AD1IF
SW Clear
(Timer and ADC Int.)
DS30009743B-page 28
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Example 5-2:
Capacitance Touch Sense with Auto-Threshold Detect ADC
#define TOUCHED 100
// expected maximum ADC counts on a touch event
void
CtmuCapTouchThreshConfig(unsigned int range, signed int trim)
{
// Step 1 Configure the port Ports
TRISB = TRISB | (6);
// Configure AN1 and AN2 as inputs
ANSBbits.ANSB2 = 1;
// Configure AN! and AN2 as analog
// Step 2 configure the CTMU
CTMUCON1L = 0x0000;
// Disable CTMU
CTMUCON1Lbits.TGEN = 0;
// Disable Time Generation mode
CTMUCON1Lbits.EDGEN = 0;
// Edges are enabled???
CTMUCON1Lbits.ITRIM = trim;
// Set trim
CTMUCON1Lbits.CTTRIG = 1;
// Trigger output enabled
CTMUCON1Lbits.IRNG = (range & 3);
// Set range
// Next line does not apply to all devices
CTMUCON1Hbits.IRNGH = (range>>2);
// set high bit of range
CTMUCON2Lbits.IRSTEN = 1;
CTMUCON2Lbits.DSCHS = 4;
// enable CTMU status reset
// end of ADC conversion resets CTMU status
CTMUCON1Lbits.CTMUEN = 1;
CTMUCON1Hbits.EDG1STAT = 1;
// enable the CTMU
// enable the current source
// Step 3 configure the ADC
IFS0bits.AD1IF = 0;
AD1CON1 = 0;
AD1CON1bits.SSRC = 5;
AD1CON1bits.ASAM = 1;
AD1CON2bits.CSCNA = 1;
AD1CON2bits.SMPI = 0;
AD1CON3bits.ADCS = 2;
AD1CON5bits.ASEN = 1;
AD1CON3bits.SAMC = 31;
AD1CON5bits.CTMREQ = 1;
AD1CON5bits.BGREQ = 1;
AD1CON5bits.ASINT = 3;
AD1CON5bits.WM = 2;
AD1CON5bits.CM = 0;
AD1CTMENL = 4;
AD1CSSL = 6;
//
//
//
//
//
//
//
//
//
//
make sure ADC Int not set
turn off ADC
Timer1 IF starts autoscan sequence
sampling begins automatically after last conversion
enable scan mode
interrupt after 1st event
ADC clock is 1/2 sys clock ???
enable autoscan
set sample time in TADs
request the CTMU
//
//
//
//
//
interrupt after a threshold event compare
do not write ADC result to buffer
compare mode: less than threshold value
Connect CTMU current source to analog channel
enable scan of AN2 & AN1
ADC1BUF1 = TOUCHED;
ADC1BUF2 = TOUCHED;
// Threshold value for A12
// Threshold value for AN2
AD1CON1bits.ADON = 1;
// Turn on the ADC
// Step 4 configure the timer
PR1 = 0xA000;
T1CONbits.TON = 1;
// set rollover rate ~10ms to trigger ADC scan
// enable timer
}
#define RANGE_5_5uA
2
// 5.5uA
2011-2016 Microchip Technology Inc.
DS30009743B-page 29
dsPIC33/PIC24 Family Reference Manual
Example 5-2:
int
{
Capacitance Touch Sense with Auto-Threshold Detect ADC (Continued)
main(void)
CtmuCapTouchThreshConfig(RANGE_5_5uA, 15);
TRISDbits.TRISD1 = 0;
RPOR12 = 13;
TRISDbits.TRISD1 = 0;
// map OCMP1 output to pin 76
// make pin an output
while(1)
{
if (IFS0bits.T1IF == 1)
{
IFS0bits.T1IF = 0;
}
LATDbits.LATD1 = 0;
// step 5-8 wait for an ADC interrupt and service the event
if (IFS0bits.AD1IF)
// Wait for ADC threshold match (this can an ISR)
{
LATDbits.LATD1 = 1;
// signal threshold event
IFS0bits.AD1IF = 0;
//
// Touch event handler
if (AD1CHITL & 4)
//
{
AD1CHITL &= ~4;
//
// user code to handle touch
}
clear int
test to determine which ANx had a touch event
clear the event
event
}
}
}
DS30009743B-page 30
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
5.4
Electrostatic Discharge (ESD) Protection
When the CTMU is used for capacitive touch applications, ESD protection must be provided on the
touch input pins to protect the microcontroller and supporting circuitry. The minimum ESD protection is a series resistor, typically 1-10 kOhms (see Figure 5-4). Additional protection in the form of
TVS diodes to power and ground is recommended. The capacitance of the TVS diodes adds to the
system capacitance for the analog channel being protected, therefore, low capacitance TVS diodes
are recommended. The device power and ground traces should be sized to accommodate the
additional current from an ESD event (refer to Section 13.0 “Related Application Notes”).
Figure 5-4:
Capacitive Touch External ESD Protection Block Diagram
ANx
Touch Pad
2011-2016 Microchip Technology Inc.
RESD
(External)
DS30009743B-page 31
dsPIC33/PIC24 Family Reference Manual
6.0
MEASURING TIME WITH THE CTMU MODULE
The CTMU, in conjunction with the ADC, can be used to precisely measure the time between
2 events. The events, internal or external, enable and disable the current source charging the
ADC sample capacitor (refer to Figure 6-1 and Figure 6-2). The ADC then converts this voltage.
An external capacitor can be used if capacitance greater than the ADC sample capacitor is
required. If an external capacitor is used, firmware may need to discharge the capacitor prior to
the next measurement. The CTMU current source and capacitance calibrations should be
performed prior to measurements (refer to Section 4.1 “Current Source Calibration” and
Section 4.2 “Capacitance Calibration”).
The time measured must be such that the current source charging the capacitance, CSYSTEM,
generates a voltage that is within the linear range of the valid current source. For the smallest
time measurement, use the lowest current range and set the ADC Channel Select register
(ADxCHS) to an unused ADC channel whose corresponding pin is not connected to any circuit
board trace. This minimizes added stray capacitance, keeping the total circuit capacitance close
to that of the A/D Converter itself. If the measured delay is too long to measure with this method,
an external capacitor may be connected to an ADC channel and this channel is selected during
the measurement. If an external capacitor is used for the measurement, it should be connected
during the capacitance calibration step.
Time measurement is accomplished with the following steps:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
DS30009743B-page 32
Configure the CTMU for Edge mode (TGEN = 0).
Configure the I/O port pin as an input and enable Analog mode.
Configure the ADC for auto-sample and auto-convert.
Clear the edge status.
Enable the CTMU.
Manually discharge the capacitor (may be required for external capacitor).
Wait for an ADC interrupt (charging will be stopped by Edge 1 and Edge 2).
Clear the ADC interrupt.
Read the ADC result.
Manually discharge the capacitor (may be required for external capacitor).
Clear the edge status.
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Figure 6-1:
Time Measurement Block Diagram
AVDD
EDG1
EDG2
ena
ANx
RESD
Optional
External
Capacitor
ADC
RMUX
ADxCHS
Figure 6-2:
Time Measurement Timing Diagram
EDG1
EDG2
ANx Pin
Capacitor
Manual
Discharge
2011-2016 Microchip Technology Inc.
DS30009743B-page 33
dsPIC33/PIC24 Family Reference Manual
Example 6-1:
Time Measurement
#define RANGE_0_550uA 1
// .550uA
void
CtmuTimeConfig(unsigned int range, signed int trim)
{
// Step 1 Configure the CTMU
CTMUCON1L = 0x0000;
// Disable CTMU
CTMUCON1Lbits.TGEN = 0;
// Disable Time Generation mode
CTMUCON1Lbits.EDGEN = 1;
// Edges are enabled
CTMUCON1Lbits.ITRIM = trim;
// Set trim
CTMUCON1Lbits.CTTRIG = 1;
// Trigger output enabled
CTMUCON1Lbits.IRNG = (range & 3);
// Set range
// This line does not apply to all devices
CTMUCON1Hbits.IRNGH = (range>>2);
// set high bit of range
CTMUCON1Hbits.EDG1MOD
CTMUCON1Hbits.EDG1POL
CTMUCON1Hbits.EDG1SEL
CTMUCON1Hbits.EDG2POL
CTMUCON1Hbits.EDG2MOD
CTMUCON1Hbits.EDG2SEL
=
=
=
=
=
=
1;
1;
4;
1;
0;
3;
//
//
//
//
//
//
Edge mode
rising edge
CTED3 pin 8
polarity
level sensitive
CTED1 pin 42
CTMUCON2Lbits.IRSTEN = 1;
CTMUCON2Lbits.DSCHS = 4;
// enable reset by external trigger
// ADC end of conversion
// Step 2 Configure the port Ports
TRISBbits.TRISB12 = 1;
ANSBbits.ANSB12 = 0;
// Configure RB12 as a input CTED2
// disable analog on RB12
TRISBbits.TRISB13 = 1;
ANSBbits.ANSB13 = 0;
// Configure RB13 as a input CTED1
// disable analog on RB13
TRISBbits.TRISB2 = 1;
ANSBbits.ANSB2 = 1;
// Configure RB2 as a input
// Configure AN2 as analog
// Step 3 configure the ADC
AD1CON1 = 0x0000;
AD1CON1bits.SSRC = 4;
AD1CON2 = 0x0000;
AD1CON3 = 0x0000;
AD1CON3bits.ADCS = 8;
AD1CON5 = 0x0000;
AD1CON1bits.ADON = 1;
AD1CON1bits.ASAM = 1;
AD1CHSbits.CH0SA = 2;
//
//
//
//
//
//
Turn off ADC
CTMU is the conversion trigger source
VR+ = AVDD, V- = AVSS, Don't scan,
ADC uses system clock
conversion clock = 1xTcy
Auto-Scan disabled
// Auto-sample
// Select AN2
// Step 4 - 6 Enable the current source and stop manual discharge
CTMUCON1H &= ~0x0300;
// clear the edge status bits
CTMUCON1Lbits.CTMUEN = 1;
// Enable the CTMU
CTMUCON1Lbits.IDISSEN = 1;
// Enable Discharge
asm("NOP");
// may be required for external caps
asm("NOP");
asm("NOP");
asm("NOP");
CTMUCON1Lbits.IDISSEN = 0;
// stop discharge
}
int
{
main(void)
DS30009743B-page 34
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Example 6-1:
Time Measurement (Continued)
unsigned
int result;
CtmuTimeConfig(RANGE_0_550uA, 5);
// .550uA
while(1)
{
// Step 7: Wait for ADC interrupt
while(IFS0bits.AD1IF == 0);
{
// Steps 8-11
IFS0bits.AD1IF = 0;
// clear the interrupt
result = ADC1BUF0;
// read ADC result
CTMUCON1Lbits.IDISSEN = 1;
asm("NOP");
asm("NOP");
asm("NOP");
asm("NOP");
CTMUCON1Lbits.IDISSEN = 0;
// begin manual discharge of cap
// may be required for external caps
CTMUCON1H &= ~0x0300;
// clear the edge status bits
// stop discharge of cap
}
// user code
}
}
2011-2016 Microchip Technology Inc.
DS30009743B-page 35
dsPIC33/PIC24 Family Reference Manual
7.0
GENERATING DELAYS WITH THE CTMU MODULE
The CTMU module can be used to create delays independent of the system clock. This is
accomplished by using the CTMU in Time Generation mode to charge a capacitance, internal or
external, and using Comparator 2 to generate an EDG2 event when the capacitor voltage
reaches the desired value, as set by the CVREF module. The pulse is started by an EDG1,
internal or external, event. In this mode, the CTPLS GPIO pin is controlled by the CTMU module
and is used to generate a pulse whose width is the delay time. If desired, the Comparator 2
interrupt can be enabled to inform software that a pulse was generated. For proper operation,
the EDG1 event should be inactive before the EDG2 event occurs. Refer to Figure 7-1 and
Figure 7-2.
The combination of the comparator reference selection, the current range and the capacitance
value are used to create the desired delay period. The delay pulse width is calculated by,
T = (CSYSTEM/I) * V, where I is known from the current source calibration (see Section 4.1
“Current Source Calibration”) and V is the comparator reference input voltage.
Time measurement is accomplished with the following steps:
1.
2.
3.
4.
5.
Configure the CTMU for Time Generation mode (TGEN = 1).
Configure the comparator reference.
Configure the comparator.
Configure the I/O port pin as an input and enable Analog mode.
Enable the CTMU.
Figure 7-1:
Delay Generation Block Diagram
AVDD
ena
EDG1
EDG2
TGEN
C2INB
RESD
ADC
RMUX
ADxCHS
AVSS
Comparator
EDG2
RESD
CVREF
CCHx
DS30009743B-page 36
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Figure 7-2:
Delay Generation Timing Diagram
t1
EDG1
t2
EDG2
ANx Pin
CTPLS
2011-2016 Microchip Technology Inc.
DS30009743B-page 37
dsPIC33/PIC24 Family Reference Manual
Example 7-1:
Delay Generation
#include "p24FJ1024GB610.h"
#define RANGE_55uA 3
// 55uA
void
CtmuDelayConfig(unsigned int range, signed int trim)
{
// Step 1 Configure the CTMU
CTMUCON1L = 0x0000;
// Disable CTMU
CTMUCON1Lbits.TGEN = 1;
// Enable/Disable Time Generation mode
CTMUCON1Lbits.IDISSEN = 1;
// Current source is grounded
CTMUCON1Lbits.ITRIM = trim;
// Set trim
CTMUCON1Lbits.CTTRIG = 0;
// Trigger output disabled
CTMUCON1Lbits.IRNG = (range & 3);
// Set range
CTMUCON1Lbits.EDGEN = 1;
// Edges are enabled
CTMUCON2Lbits.IRSTEN = 0;
// Current source reset disabled
CTMUCON2Lbits.DSCHS = 0;
// Discharge source disabled
// This line does not apply to all devices
CTMUCON1Hbits.IRNGH = (range>>2);
// set high bit of range
CTMUCON1Hbits.EDG1POL = 1;
// negative polarity
CTMUCON1Hbits.EDG1MOD = 1;
// edge sensitve
CTMUCON1Hbits.EDG1SEL = 4;
// CTED3 pin 8
CTMUCON1Hbits.EDG2POL = 1;
// negative polarity
CTMUCON1Hbits.EDG2MOD = 0;
// level sensitive
CTMUCON1Hbits.EDG2SEL = 14;
// CMP2 out
// Step 2 Configure Comparator Voltage Reference
CVRCONbits.CVREFP = 0;
// use DAC as module output
CVRCONbits.CVROE = 1;
// DAC voltage is output on a pin
CVRCONbits.CVRSS = 0;
// DAC references are AVDD/AVSS
CVRCONbits.CVR = 14;
// midscale output
CVRCONbits.CVREN = 1;
// enable module
// Step 3 Configure Comparator
CM2CONbits.COE = 1;
CM2CONbits.CPOL = 1;
CM2CONbits.CREF = 1;
CM2CONbits.CCH = 0;
CM2CONbits.CEN = 1;
//
//
//
//
//
comparator output is present on C2OUT pin
output is inverted
non-inverting input is CVREF output
inverting input is C2INB pin
enable the comparator
// Step 2 Configure the port Ports
TRISBbits.TRISB2 = 1;
// Configure RB2 as a input
ANSBbits.ANSB2 = 1;
// Configure AN2 as analog
// (Capacitor to AVSS is connected to this pin)
TRISGbits.TRISG15 = 1;
// Configure RG15 (CTED3 as an input)
CTMUCON1Lbits.CTMUEN = 1;
// Enable the CTMU
}
int
{
main(void)
CtmuDelayConfig(RANGE_55uA, 6);
// external event triggers EDG1
// user code
while(1);
}
DS30009743B-page 38
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
8.0
MEASURING TEMPERATURE WITH THE CTMU
The CTMU module can be used to measure the internal temperature of the device through a
dedicated internal temperature diode. When configured for temperature measurement, the
CTMU current flows through the diode. The resulting voltage drop across the diode can then be
measured with the ADC and the temperature calculated.
The Forward Voltage (Vf) of a P-N diode changes with temperature. The Forward Voltage (Vf) of
a diode is negatively proportional to the temperature. In other words, Vf increases with a
decrease in temperature. Temperature measurements should only be performed with the CTMU
at the 5.5 µA or 55 µA current ranges.
Figure 8-1 shows how this module can be used for temperature measurement. As the temperature
rises, the voltage across the diode will drop approximately 1.8 mV/°C (for the 5.5 µA range) over
the device operating range (refer to Figure 8-2, Equation 8-1 and Example 8-2). Using the 55 µA
current range increases the voltage offset, providing an improvement in signal to noise ratio. The
voltage output of the diode is nearly linear across the device specified operating range for both
ranges.
Figure 8-1:
Temperature Measurement Block Diagram
AVDD
EDG1
EDG2
Internal
Diode
ena
ADC
RMUX
ADxCHS
Note:
Refer to the specific device data sheet for the actual channel number associated with the
temperature sensing diode.
2011-2016 Microchip Technology Inc.
DS30009743B-page 39
dsPIC33/PIC24 Family Reference Manual
Diode Voltage (mV)
Figure 8-2:
Temperature Curves
850
825
800
775
750
725
700
675
650
625
600
575
550
525
500
475
450
5.5
µA
5.5UA
55
µA
55UA
-40
-20
0
20
40
60
80
100
120
Die Temperature (°C)
8.1
Operation
When the current source is enabled, TGEN = 0, and the temperature diode is selected as the
ADC analog input, the CTMU current source output is connected to the temperature sensing
diode. The voltage developed across the diode is available as an input to the ADC module
through a dedicated analog input channel, which is selected using ADxCHS register (refer to
Example 8-1).
The following outlines the steps required to perform a temperature measurement:
1.
2.
3.
4.
5.
6.
DS30009743B-page 40
Configure and enable the CTMU.
Configure the ADC.
Start manual sampling.
Wait for sample capacitor to charge.
Convert sample.
Convert counts to temperature (refer to Equation 8-1).
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
Example 8-1:
#define
Temperature Measurement
RANGE_5_5uA
2
// 5.5uA
unsigned
int CtmuReadTemperatureCounts(unsigned int range, signed int trim)
{
unsigned
int x, result;
// Step 1 Configure the CTMU
CTMUCON1L = 0x0000;
CTMUCON1Lbits.ITRIM = trim;
CTMUCON1Lbits.IRNG = (range & 3);
CTMUCON1Lbits.CTMUEN = 1;
CTMUCON1Hbits.EDG1STAT = 1;
CTMUCON1Hbits.EDG2STAT = 1;
// Disable CTMU
// Set trim
// Set range
// Enable the CTMU
// Enable current source
// Step 2 Configure the ADC
AD1CHSbits.CH0SA = 0x18;
// Select temp sensor
AD1CON1 = 0x8000;
// Turn On A/D Converter,
// Unsigned fractional format, Clear SAMP bit to
// start conversion, Sample when SAMP bit is set
AD1CON2 = 0x0000;
// VR+ = AVDD, V- = AVSS, Don't scan,
AD1CON3 = 0x0000;
// ADC uses system clock
AD1CON3bits.ADCS = 0;
// conversion clock = 1xTcy
AD1CON5 = 0x0000;
// Auto-Scan disabled
AD1CTMENHbits.CTMEN24 = 1;
// CTMU connected to channel during conversion
// Step 3 start sampling
AD1CON1bits.SAMP = 1;
// Manual sampling start
// Step 4 delay
for (x = 0; x < 2000; x++);
// Delay ~xxx us to charge sample cap
// step 5 convert sample
AD1CON1bits.SAMP = 0;
while(AD1CON1bits.DONE == 0);
// Begin A/D conversion
// Wait for A/D convert complete
result = ADC1BUF0;
return (result);
}
int
{
main(void)
unsigned
int result;
result = CtmuReadTemperatureCounts( RANGE_5_5uA, 6);
while(1);
}
2011-2016 Microchip Technology Inc.
DS30009743B-page 41
dsPIC33/PIC24 Family Reference Manual
Equation 8-1:
CTMU Temperature Measurement Calculations
For 5.5 µA Current Source Range:
TINTERNAL =
710 mV – VMEASURED
1.8
For 55 µA Current Source Range:
TINTERNAL =
760 mV – VMEASURED
1.55
VMEASURED = ADC Counts * ADC Reference/ADC Max Counts
Example 8-2:
CTMU Temperature Measurement Calculations
ADC in 10-Bit Mode, ADC Reference 3.3V
ADC Measured Counts = 0xCC = 204 Decimal
CTMU Configured for 5.5 µA Range
VMEASURED = ADC Counts * ADC Reference/ADC Max Counts
VMEASURED = 204c * 3.3V/1023 = 657 mV
TINTERNAL =
DS30009743B-page 42
710 mV – 658 mV
= 28.9C
1.8
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
8.2
Calibration
The accuracy of the temperature measurement can be improved with a calibration process.
For narrow temperature measurement ranges, calculating the theoretical voltage, and comparing
it to the measured voltage at a known temperature, will give a calibration offset that can be used
for future measurements.
For wide temperature measurement ranges, a measurement is required at two known temperatures to more accurately calculate an offset. Ideally, these measurements are near the extremes of
the desired measurement range. The results of these two measurements are first used to calculate
the temperature curve slope. The resulting slope is then used in the temperature equation to
calculate an offset (refer to Equation 8-2). This offset then can be added or subtracted from future
measurements.
The temperature calibration compensates for the CTMU current, therefore, current source calibration is not required for temperature calibration. If the current source calibration is required for
other applications, the temperature calibration should be performed after the current source is
calibrated.
Equation 8-2:
Temperature Slope Calculations
Slope =
(Temperature1 – Temperature2)
Voltage at t1 – Voltage at t2
Offset in Volts = Temperature1 – (Slope * Voltage at t1)
Volts/ADC Count =
ADC Reference Voltage
(2^ADC Bits)
Temperature = (Voltage/Slope) + Offset
Example 8-3:
Temperature Calibration
t1 = 40°C, 242 ADC Counts
t2 = 120°C, 150 ADC Counts
CTMU Configured for 5.5 µA Range
ADCres =
Slope =
3.3V
= 3.22 mV/Count = 0.00322
1023 Counts
0.296
(242c – 150c) * 0.00322
=
= 0.00186 = 1.86 mV/°C
-160
-40 – 120
Offset = -40°C –
(0.00322 * 242)
= -378.8
-0.00186
Therefore, for a Measurement of 195 Counts:
T=
2011-2016 Microchip Technology Inc.
(195 * 0.00322)
– 378.8 = 40.5°C
0.00186
DS30009743B-page 43
dsPIC33/PIC24 Family Reference Manual
9.0
OPERATION DURING SLEEP/IDLE MODES
9.1
Sleep Mode and Deep Sleep Modes with the CTMREQ Bit
Disabled and Devices without a CTMREQ Bit
When the device enters any Sleep mode, the CTMU module current source is always disabled.
If the CTMU is performing an operation that depends on the current source when Sleep mode is
invoked, the operation may not terminate correctly. Capacitance and time measurements may
return erroneous values.
9.2
Sleep Mode and Deep Sleep Modes with the CTMREQ Bit Enabled
When the device enters Sleep mode with the CTMREQ bit (ADxCON5<13>) set, the CTMU will
continue operation in Sleep. The CTMU can be triggered from the ADC, which can perform the
conversion in Sleep mode when the A/D clock source is set to the internal A/D RC oscillator
(ADRC = 1). This will allow the CPU to remain in the inactive state for a longer period of time,
and at the same time, it can perform the conversion of the selected CTMU channel.
When the A/D interrupt (AD1IE) is enabled, the device will wake-up from Sleep as soon as the
A/D interrupt occurs. This will help to reduce the power consumed by the CPU, which is the
prerequisite for many low-power applications.
9.3
Idle Mode
The behavior of the CTMU in Idle mode is determined by the CTMUSIDL bit (CTMUCON1L<13>).
If CTMUSIDL is cleared, the module will continue to operate in Idle mode. If CTMUSIDL is set,
the module’s current source is disabled when the device enters Idle mode. If the module is
performing an operation when Idle mode is invoked, in this case, the results will be similar to
those with Sleep mode.
DS30009743B-page 44
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
10.0
EFFECTS OF A RESET ON CTMU
Upon Reset, all registers of the CTMU are cleared. This leaves the CTMU module disabled, its
current source is turned off and all configuration options return to their default settings. The
module needs to be re-initialized following any Reset.
If the CTMU is in the process of taking a measurement at the time of Reset, the measurement will
be lost.
11.0
LOW-POWER APPLICATIONS FOR DEVICES WITH A CTMREQ BIT
The CTMU module, along with the ADC with Auto-Threshold Detection technique, can be used
for implementing low-power based applications. The low-power functionality can be achieved by
alternatively shifting between the Normal mode and the Sleep mode, which is based on the need
of the application. The CTMU module will be active in Sleep mode by enabling the CTMREQ bit
(ADxCON5<13>). This logic will significantly reduce the power consumed by the system, which
is the common requirement in many of the applications.
12.0
ELECTRICAL SPECIFICATIONS
Refer to the device data sheet “Electrical Characteristics” section for the current ranges for
your device.
2011-2016 Microchip Technology Inc.
DS30009743B-page 45
dsPIC33/PIC24 Family Reference Manual
13.0
RELATED APPLICATION NOTES
This section lists application notes and technical briefs that are related to this section of the
manual. These application notes and technical briefs may not be written specifically for the
dsPIC33/PIC24 device families, but the concepts are pertinent and could be used with modification and possible limitations. The current application notes and technical briefs related to the
Charge Time Measurement Unit (CTMU) and CTMU Operation with Threshold Detect module
are:
Title
Application Note #
See What You Can do with the CTMU
®
AN1375
Using the PIC MCU CTMU for Temperature Measurement
TB3016
Microchip CTMU for Capacitive Touch Applications
AN1250
ESD and EOS Causes, Differences and Prevention
AN1785
Techniques for Robust Touch Sensing Design
AN1334
mTouch™ Conducted Noise Immunity Techniques for the CTMU
AN1317
Source Code for PIC24F MCU using CTMU Sensing Method – PIC24F source code and projects
for touch sensing, in conducted noise environment, using the CTMU and ADC for sensing.
Note:
DS30009743B-page 46
Please visit the Microchip web site (www.microchip.com) for additional application
notes and code examples for the dsPIC33/PIC24 families of devices.
2011-2016 Microchip Technology Inc.
CTMU and CTMU Operation with Threshold Detect
14.0
REVISION HISTORY
Revision A (March 2011)
This is the initial released revision of this document.
Revision B (April 2016)
The document was updated to include the dsPIC33 families of devices and the title was changed
to CTMU and CTMU Operation with Threshold Detect. Updated the Family Reference Manual
name to dsPIC33/PIC24 Family Reference Manual. Removed Section 53 and tabs as this family
reference manual does not use overall section numbers. Headings were renumbered
appropriately.
• Equations:
- Added Equation 4-1, Equation 4-2, Equation 4-3, Equation 4-4, Equation 4-5,
Equation 8-1 and Equation 8-2
• Examples:
- Added Example 4-1, Example 4-2, Example 4-3, Example 4-4, Example 4-5,
Example 5-1, Example 5-2, Example 6-1, Example 7-1, Example 8-1, Example 8-2
and Example 8-3
• Figures:
- Updated Figure 1-1
- Added Figure 1-2, Figure 4-1, Figure 4-2, Figure 4-3, Figure 5-1, Figure 5-2,
Figure 5-3, Figure 5-4, Figure 6-1, Figure 6-2, Figure 7-1, Figure 7-2, Figure 8-1 and
Figure 8-2
• Tables:
- Removed previous Table 53-2
- Updated Table 2-1
- Added Table 4-1
• Registers:
- Updated Register 2-1, Register 2-2 and Register 2-3
• Sections:
- Removed previous Sections 53.4 through 53-9
- Updated Section 1.0 “Introduction”, Section 2.0 “Register Maps”, Section 9.0
“Operation During Sleep/Idle Modes”, Section 10.0 “Effects of a Reset on
CTMU”, Section 11.0 “Low-Power Applications for Devices with a CTMREQ Bit”,
Section 12.0 “Electrical Specifications” and Section 13.0 “Related Application
Notes”
- Added completely new Section 3.0 “CTMU Operation” through Section 8.0
“Measuring Temperature with the CTMU”
• Additional minor corrections such as language and formatting updates were incorporated
throughout the document
2011-2016 Microchip Technology Inc.
DS30009743B-page 47
dsPIC33/PIC24 Family Reference Manual
NOTES:
DS30009743B-page 48
2011-2016 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights unless otherwise stated.
Trademarks
The Microchip name and logo, the Microchip logo, AnyRate,
dsPIC, FlashFlex, flexPWR, Heldo, JukeBlox, KeeLoq,
KeeLoq logo, Kleer, LANCheck, LINK MD, MediaLB, MOST,
MOST logo, MPLAB, OptoLyzer, PIC, PICSTART, PIC32 logo,
RightTouch, SpyNIC, SST, SST Logo, SuperFlash and UNI/O
are registered trademarks of Microchip Technology
Incorporated in the U.S.A. and other countries.
ClockWorks, The Embedded Control Solutions Company,
ETHERSYNCH, Hyper Speed Control, HyperLight Load,
IntelliMOS, mTouch, Precision Edge, and QUIET-WIRE are
registered trademarks of Microchip Technology Incorporated
in the U.S.A.
Analog-for-the-Digital Age, Any Capacitor, AnyIn, AnyOut,
BodyCom, chipKIT, chipKIT logo, CodeGuard, dsPICDEM,
dsPICDEM.net, Dynamic Average Matching, DAM, ECAN,
EtherGREEN, In-Circuit Serial Programming, ICSP, Inter-Chip
Connectivity, JitterBlocker, KleerNet, KleerNet logo, MiWi,
motorBench, MPASM, MPF, MPLAB Certified logo, MPLIB,
MPLINK, MultiTRAK, NetDetach, Omniscient Code
Generation, PICDEM, PICDEM.net, PICkit, PICtail,
PureSilicon, RightTouch logo, REAL ICE, Ripple Blocker,
Serial Quad I/O, SQI, SuperSwitcher, SuperSwitcher II, Total
Endurance, TSHARC, USBCheck, VariSense, ViewSpan,
WiperLock, Wireless DNA, and ZENA are trademarks of
Microchip Technology Incorporated in the U.S.A. and other
countries.
SQTP is a service mark of Microchip Technology Incorporated
in the U.S.A.
Microchip received ISO/TS-16949:2009 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
QUALITY MANAGEMENT SYSTEM
CERTIFIED BY DNV
== ISO/TS 16949 ==
2011-2016 Microchip Technology Inc.
Silicon Storage Technology is a registered trademark of
Microchip Technology Inc. in other countries.
GestIC is a registered trademarks of Microchip Technology
Germany II GmbH & Co. KG, a subsidiary of Microchip
Technology Inc., in other countries.
All other trademarks mentioned herein are property of their
respective companies.
© 2011-2016, Microchip Technology Incorporated, Printed in
the U.S.A., All Rights Reserved.
ISBN: 978-1-5224-0493-4
DS30009743B-page 49
Worldwide Sales and Service
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07/14/15
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2011-2016 Microchip Technology Inc.