RM0313 Datasheet, PDF (747/900 Pages) STMicroelectronics – This reference manual targets application developers

RM0313
Touch sensing controller (TSC)
27.3.4
Charge transfer acquisition sequence
An example of a charge transfer acquisition sequence is detailed in Figure 261.
Figure 261. Charge transfer acquisition sequence
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#_{8 (I:}


#_{3 (I:}

#HARGETRANSFERFREQUENCY
3TATE
$ISCHARGE
#₈AND#₃
0ULSEHIGHSTATE
CHARGEOF#₈
0ULSELOWSTATE
CHARGETRANSFER
FROM#₈TO#₃
T
-36
For higher flexibility, the charge transfer frequency is fully configurable. Both the pulse high
state (charge of C_X) and the pulse low state (transfer of charge from C_X to C_S) duration can
be defined using the CTPH[3:0] and CTPL[3:0] bits in the TSC_CR register. The standard
range for the pulse high and low states duration is 500 ns to 2 µs. To ensure a correct
measurement of the electrode capacitance, the pulse high state duration must be set to
ensure that C_X is always fully charged.
A dead time where both the sampling capacitor I/O and the channel I/O are in input floating
state is inserted between the pulse high and low states to ensure an optimum charge
transfer acquisition sequence. This state duration is 2 periods of HCLK.
At the end of the pulse high state and if the spread spectrum feature is enabled, a variable
number of periods of the SSCLK clock are added.
The reading of the sampling capacitor I/O, to determine if the voltage across C_S has
reached the given threshold, is performed at the end of the pulse low state and its duration
is one period of HCLK.
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