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C28 General-Purpose Input/Output (GPIO)
4.2.5 Input Qualification
The input qualification scheme has been designed to be very flexible. You can select the type of input
qualification for each GPIO pin by configuring the GPxQSEL1 and GPxQSEL2 registers. In the case of a
GPIO input pin, the qualification can be specified as only synchronize to SYSCLKOUT or qualification by a
sampling window. For pins that are configured as peripheral inputs, the input can also be asynchronous in
addition to synchronized to SYSCLKOUT or qualified by a sampling window. The remainder of this section
describes the options available.
4.2.5.1
No Synchronization (asynchronous input)
This mode is used for peripherals where input synchronization is not required or the peripheral itself
performs the synchronization. Examples include communication ports SCI, SPI and I
be desirable to have the ePWM trip zone (TZn) signals function independent of the presence of
SYSCLKOUT.
The asynchronous option is not valid if the pin is used as a general purpose digital input pin (GPIO). If the
pin is configured as a GPIO input and the asynchronous option is selected then the qualification defaults
to synchronization to SYSCLKOUT as described in
4.2.5.2
Synchronization to SYSCLKOUT Only
This is the default qualification mode of all the pins on GPIO Port A, B, and C. The GPIO pins on Port E
are synchronized to the analog subsystem clock by default. In this mode, the input signal is only
synchronized to the system clock (SYSCLKOUT). Because the incoming signal is asynchronous, it can
take up to a SYSCLKOUT period of delay in order for the input to the DSP to be changed. No further
qualification is performed on the signal.
4.2.5.3
Qualification Using a Sampling Window
In this mode, the signal is first synchronized to the system clock (SYSCLKOUT) and then qualified by a
specified number of cycles before the input is allowed to change.
the input qualification is performed to eliminate unwanted noise. Two parameters are specified by the user
for this type of qualification: 1) the sampling period, or how often the signal is sampled, and 2) the number
of samples to be taken.
GPIOx
Time between samples (sampling period):
To qualify the signal, the input signal is sampled at a regular period. The sampling period is specified by
the user and determines the time duration between samples, or how often the signal will be sampled,
relative to the CPU clock (SYSCLKOUT).
380
General-Purpose Input/Output (GPIO)
Figure 4-40. Input Qualification Using a Sampling Window
SYNC
SYSCLKOUT
Copyright © 2012–2019, Texas Instruments Incorporated
Section
4.2.5.2.
Figure 4-40
Time between samples
GPxCTRL Reg
Qualification
GPxQSEL1/2
Number of Samples
SPRUH22I – April 2012 – Revised November 2019
www.ti.com
2
C. In addition, it may
and
Figure 4-41
show how
Input Signal
Qualified By 3
or 6 Samples
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