Design Considerations
CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
53
Figure 5-2. Recommended Port Isolation for Communication, CapSense, and LEDs
All GPIOs of the CapSense controller are capable of implementing the CapSense sensor and drive LEDs. However, if
the GPIOs LED drive and CapSense sensors are implemented in the same project, it is recommended to use GPIO
according to
for best performance. If a design is implementing only CapSense sensors or only LED drive,
the restrictions mentioned in
Table 5-5. Recommended GPIOs for LED Drive and CapSense Sensors
Recommended for LED Drive
Recommended for CapSense Sensors and CMOD
P0.1, P2.5, P2.3, P2.1, P4.1, P3.7, P3.5,
P3.3, P3.1, P1.7, P1.5, P1.3, P1.1
P1.0, P1.2, P1.4, P1.6, P3.0, P3.2, P3.4, P3.6, P4.0,
P4.2, P2.0, P2.2, P2.4, P0.0, P0.2, P0.4, P0.6, P0.3
The architecture of the CapSense controller imposes a restriction on current budget for even and odd port pin
numbers. An odd pin can be any port pin having an odd number as pin number. For a CapSense controller, if the
current budget of odd port pin is 100 mA, the total current drawn though all odd port pins should not exceed 100 mA.
In addition to the total current budget limitation, there is also a maximum current limitation for each port pin that is
defined in the CapSense controller datasheet.
All CapSense controllers provide high-current sink and source capable port pins. When using high-current sink or
source from port pins, it is recommended to use the ports that are closest to device ground pin to minimize the noise.
5.7 GPIO Load Transient
When GPIOs sink a large current (>10 mA) to the ground of the chip by driving port pins to strong-low, noise will be
introduced into the CapSense system. The instantaneous change in the amount of the current flow to ground through
the GPIOs is referred as GPIO load transient. The noise introduced into the CapSense system due to the GPIO load
transient is called GPIO load transient noise, as shown in
. This section shows you how to reduce the
GPIO load transient noise using hardware techniques, and compensate the noise using firmware techniques.
