86
PSoC CY8CTMG20x and CY8CTST200 TRM, Document No. 001-53603 Rev. *C
TrueTouch Module
The circuit operates by alternately charging the sense
capacitance to the internal voltage buffer level (first phase),
then on the opposite phase of the clock (second phase), the
analog global bus is connected to the integration capacitor
while the voltage buffer is disconnected. (See
This builds up voltage on the integration capacitor, and
eventually it trips the monitoring comparator. The compara-
tor is configured to capture the number of counts of the inter-
nal oscillator during the charging interval, yielding a
capacitance measurement of the sense pin.
Figure 11-3. Charging the TrueTouch and Connection
11.1.1.2
Relaxation Oscillator
The relaxation oscillator (RO) method operates by forming
an oscillator using the sense capacitance. The IDAC, sense
capacitance, and comparator (switching between two refer-
ences) form the RO. There are two RO methods of capsens-
ing supported.
In the first method, the RO is compared to the frequency of a
similar internal oscillator. Normally, the relaxation oscillator
is initially tuned (through firmware) to match the internal
oscillator or to match a submultiple of the internal oscillator.
The frequency difference is measured by defining an interval
of internal oscillator clocks and counting the number of RO
periods that occur during this interval. (See
.)
Two 8-bit counters are used: one clocked by the internal
oscillator and one clocked by the relaxation oscillator.
With the RO frequency closely matched to the internal oscil-
lator and the interval set to 256 clocks, the 8-bit RO count
result is the difference between the two oscillators. An over-
flow bit is available to test whether the number of capture
counts is greater than or less than 256. Other count intervals
are available. (See
Figure 11-4. Relaxation Oscillator #1 Block Diagram
In the second RO method, the interval is set by a number of
cycles of the RO using a 6-bit counter. During this interval,
the IMO clocks a 16-bit counter and the final count gives a
measure of capacitance. (See
Reference
Buffer
Vr
C
EXTERNAL
P0[1]
or
P0[3]
Analo
g G
lobal
Bu
s
Comparator
Mux
Mux
Vref
Closed
Closed
Reference
Buffer
Vr
Analo
g Gl
obal
Bu
s
Comparator
Mux
Mux
Vref
Closed
Open
Closed
Open
First Phase: Charging the Sense Capacitor CS1
Second Phase: Integrating Charge onto
Integration Capacitor
CSCLK
Pin Enables
CSCLK
C
EXTERNAL
P0[1]
or
P0[3]
Pin Enables
CSCLK
CSCLK
CS1
CS2
CSN
CS1
CS2
CSN
IDAC
A
nalo
g
G
loba
l B
us
Comparator
Mux
Mux
Refs
TrueTouch
Clock Select
RO Clock
IMO
CSCLK
Pin Enables
TrueTouch Logic
8-Bit Counter
8-Bit Counter
CS1
CS2
CSN
Содержание PSoC CY8CTMG20 Series
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Страница 26: ...26 PSoC CY8CTMG20x and CY8CTST200 TRM Document No 001 53603 Rev C Section B PSoC Core Feedback...
Страница 54: ...54 PSoC CY8CTMG20x and CY8CTST200 TRM Document No 001 53603 Rev C Interrupt Controller Feedback...
Страница 62: ...62 PSoC CY8CTMG20x and CY8CTST200 TRM Document No 001 53603 Rev C General Purpose I O GPIO Feedback...
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