4.4 Input Qualification
4.4.1 No Synchronization (asynchronous input)
4.4.2 Synchronization to SYSCLKOUT Only
4.4.3 Qualification Using a Sampling Window
GPxCTRL Reg
SYNC
SYSCLKOUT
Qualification
Input Signal
Qualified By 3
or 6 Samples
GPIOx
Time between samples
GPxQSEL1/2
Number of Samples
Input Qualification
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Writing a 0 to any bit in the toggle registers has no effect.
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 GPAQSEL1, GPAQSEL2, GPBQSEL1 and GPBQSEL2
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.
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, eCAN, and I2C. In
addition, it may be desirable to have the ePWM trip zone ( TZ1- TZ6) 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 Section 4.4.2 .
This is the default qualification mode of all the pins at reset. 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.
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. Figure 4-6 and Figure 4-7 show how 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.
Figure 4-6. Input Qualification Using a Sampling Window
74 General-Purpose Input/Output (GPIO) SPRUFB0C – September 2007 – Revised May 2009
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