Input Qualification Using A Sampling Window; Sampling Period; Sampling Frequency - Texas Instruments Concerto F28M36 Series Technical Reference Manual

C28 General-Purpose Input/Output (GPIO)
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).
The sampling period is specified by the qualification period (QUALPRDn) bits in the GPxCTRL register.
The sampling period is configurable in groups of 8 input signals. For example, GPIO0 to GPIO7 use
GPACTRL[QUALPRD0] setting and GPIO8 to GPIO15 use GPACTRL[QUALPRD1].
Table 4-40 show the relationship between the sampling period or sampling frequency and the
GPxCTRL[QUALPRDn] setting.
If GPxCTRL[QUALPRDn] = 0
If GPxCTRL[QUALPRDn] ≠ 0
If GPxCTRL[QUALPRDn] = 0
If GPxCTRL[QUALPRDn] ≠ 0
From these equations, the minimum and maximum time between samples can be calculated for a given
SYSCLKOUT frequency:
Example: Maximum Sampling Frequency:
If GPxCTRL[QUALPRDn] = 0
then the sampling frequency is f
If, for example, f
then the signal will be sampled at 150 MHz or one sample every 6.67 ns.
390
General-Purpose Input/Output (GPIO)
Figure 4-40. Input Qualification Using a Sampling Window
SYNC
SYSCLKOUT
Table 4-39. Sampling Period

Sampling Period

1 × T
2 × GPxCTRL[QUALPRDn] × T
Where T
Table 4-40. Sampling Frequency

Sampling Frequency

f
SYSCLKOUT
f
SYSCLKOUT
Where f
SYSCLKOUT
= 150 MHz
SYSCLKOUT
Copyright © 2012–2019, Texas Instruments Incorporated
Time between samples
GPxCTRL Reg
Qualification
GPxQSEL1/2
Number of Samples
SYSCLKOUT
SYSCLKOUT
is the period in time of SYSCLKOUT
SYSCLKOUT
× 1 ÷ (2 × GPxCTRL[QUALPRDn])
is the frequency of SYSCLKOUT
SYSCLKOUT
SPRUHE8E – October 2012 – Revised November 2019
www.ti.com
Input Signal
Qualified By 3
or 6 Samples
Table 4-39 and
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