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CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
I/O Analog Multiplexer
Figure 33-3. Dual Channel IDAC
Therefore this IDAC block supports two different operation
modes, depending on ‘ICEN’ bit setting.
33.2
PSoC Device Distinctions
The CY8C28x03 and CY8C28x23 PSoC devices differ from
the other CY8C28xxx devices in that they do not have a
chip-wide, internal analog bus that can connect to every
GPIO. The CY8C28x13, CY8C28x33, CY8C28x43,
CY8C28x45, and CY8C28x52 device groups do have an
analog mux bus. In the CY8C28xxx device groups that have
I/O analog mux capability, all GPIO pins are enabled for this
connection.
33.3
Application Description
The analog mux circuitry enables a variety of unique appli-
cations such as those explained in the following sections.
33.3.1
Capacitive Sensing
The analog mux supports capacitive sensing applications
through the use of the I/O analog multiplexer and its control
circuitry. Two off-chip capacitors are normally connected to
the analog mux bus. One is the sense capacitor being mea-
sured and the other is an integration capacitor that accumu-
lates charge from the sense capacitor. The integration
capacitor is initialized (low) under firmware control, using its
pin’s GPIO cell. After that, the capacitor is charged through
charge-sharing with the sense capacitor.
The sense capacitor can be automatically initialized and
sensed for a number of cycles, to build up sufficient charge
on the integration capacitor. Several clocking choices are
available for selection in the AMUX_CFG register. The
circuitry is contained in each pin’s mux
so that each cycle’s initialization of the sense capacitor does
not disturb the internal bus. In the CY8C28x13, CY8C28x33,
CY8C28x45, and CY8C28x52 PSoC devices, the sense
capacitor is discharged to Vss and then released and recon-
nected to the analog mux for charge transfer from the inte-
0 1
0 1
1 0
(IDAC0_D)
(IDAC1_D)
On/Off
switch
ICEN
(IDAC_CR1)
IDAC
Left
IDAC
Right
Mux
Bus
Right
Mux
Bus
Left
iunit
iunit
ioutR
On/Off
switch
1 0
ioutL
(AMuxBus1)
(AMuxBus0)
Table 33-1. IDAC Operation Mode
Normal Mode
ICEN = 0
Left channel output current is decided by
IDAC0_D register. Right channel output cur-
rent is decided by IDAC1_D register. Both of
them can be cut off depending on their switch
ON/OFF signal.
Compensation
Mode
ICEN = 1
The switches won’t be cut off even the switch
control signal is OFF. Both channels will out-
put current based on IDAC0_D when the cor-
responding switch is ON. Both channels will
output current based on IDAC1_D when the
corresponding switch is OFF.
Summary of Contents for CY8C28 series
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