CY8C3865LTI-059 datasheet(38/129 Pages) CYPRESS

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PSoC® 3: CY8C38 Family

Data Sheet

Document Number: 001-11729 Rev. *R

Page 38 of 129

6.4.8 Analog Connections

These connections apply only to GPIO pins. All GPIO pins may

be used as analog inputs or outputs. The analog voltage present

on the pin must not exceed the Vddio supply voltage to which the

GPIO belongs. Each GPIO may connect to one of the analog

global busses or to one of the analog mux buses to connect any

pin to any internal analog resource such as ADC or comparators.

In addition, select pins provide direct connections to specific

analog features such as the high current DACs or uncommitted

opamps.

6.4.9 CapSense

This section applies only to GPIO pins. All GPIO pins may be

used to create CapSense buttons and sliders[16]. See the

“CapSense” section on page 59 for more information.

6.4.10 LCD Segment Drive

This section applies only to GPIO pins. All GPIO pins may be

used to generate Segment and Common drive signals for direct

glass drive of LCD glass. See the “LCD Direct Drive” section on

page 58 for details.

6.4.11 Adjustable Output Level

This section applies only to SIO pins. SIO port pins support the

ability to provide a regulated high output level for interface to

external signals that are lower in voltage than the SIO’s

respective Vddio. SIO pins are individually configurable to output

either the standard Vddio level or the regulated output, which is

based on an internally generated reference. Typically a voltage

DAC (VDAC) is used to generate the reference (see Figure

6-12). The “DAC” section on page 59 has more details on VDAC

use and reference routing to the SIO pins. Resistive pullup and

pull-down drive modes are not available with SIO in regulated

output mode.

6.4.12 Adjustable Input Level

This section applies only to SIO pins. SIO pins by default support

the standard CMOS and LVTTL input levels but also support a

differential mode with programmable levels. SIO pins are

grouped into pairs. Each pair shares a reference generator block

which, is used to set the digital input buffer reference level for

interface to external signals that differ in voltage from Vddio. The

reference sets the pins voltage threshold for a high logic level

(see Figure 6-12). Available input thresholds are:

0.5

× Vddio

0.4

× Vddio

0.5

× VREF

VREF

Typically a voltage DAC (VDAC) generates the VREF reference.

“DAC” section on page 59 has more details on VDAC use and

reference routing to the SIO pins.

Figure 6-12. SIO Reference for Input and Output

6.4.13 SIO as Comparator

This section applies only to SIO pins. The adjustable input level

feature of the SIOs as explained in the Adjustable Input Level

section can be used to construct a comparator. The threshold for

the comparator is provided by the SIO's reference generator. The

reference generator has the option to set the analog signal

routed through the analog global line as threshold for the

comparator. Note that a pair of SIO pins share the same

threshold. The digital input path in Figure 6-9 on page 35

illustrates this functionality. In the figure, ‘Reference level’ is the

analog signal routed through the analog global. The hysteresis

feature can also be enabled for the input buffer of the SIO, which

increases noise immunity for the comparator.

6.4.14 Hot Swap

This section applies only to SIO pins. SIO pins support ‘hot swap’

capability to plug into an application without loading the signals

that are connected to the SIO pins even when no power is

applied to the PSoC device. This allows the unpowered PSoC to

maintain a high impedance load to the external device while also

preventing the PSoC from being powered through a GPIO pin’s

protection diode.

Note

16. GPIOs with opamp outputs are not recommended for use with CapSense.

Drive

Logic

Driver

Vhigh

Reference

Generator

SIO_Ref

Digital

Input

Digital

Output

Input Path

Output Path

Vinref

Voutref

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