Sampling Period; Sampling Frequency - Texas Instruments Concerto F28M35 Series Technical Reference Manual

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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 4-41 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.
Example: Minimum Sampling Frequency:
If GPxCTRL[QUALPRDn] = 0xFF (i.e. 255)
then the sampling frequency is f
If, for example, f
then the signal will be sampled at 150 MHz × 1 ÷ (2 × 255) or one sample every 3.4 μs.
Number of samples:
The number of times the signal is sampled is either three samples or six samples as specified in the
qualification selection (GPxQSEL1 and GPxQSEL2, registers). When three or six consecutive cycles are
the same, then the input change will be passed through to the DSP.
Total Sampling Window Width:
The sampling window is the time during which the input signal will be sampled as shown in
By using the equation for the sampling period along with the number of samples to be taken, the total
width of the window can be determined.
For the input qualifier to detect a change in the input, the level of the signal must be stable for the duration
of the sampling window width or longer.
The number of sampling periods within the window is always one less then the number of samples taken.
For a thee-sample window, the sampling window width is 2 sampling periods wide where the sampling
period is defined in
sampling periods wide.
the total sampling window width based on GPxCTRL[QUALPRDn] and the number of samples taken.
SPRUH22I – April 2012 – Revised November 2019
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Table 4-40. Sampling Period

Sampling Period

1 × T
2 × GPxCTRL[QUALPRDn] × T
Where T
Table 4-41. Sampling Frequency

Sampling Frequency

f
SYSCLKOUT
f
SYSCLKOUT
Where f
SYSCLKOUT
= 150 MHz
SYSCLKOUT
× 1 ÷ (2 × GPxCTRL[QUALPRDn])
SYSCLKOUT
= 150 MHz
SYSCLKOUT
Table 4-40. Likewise, for a six-sample window, the sampling window width is 5
Table 4-42 and Table 4-43
Copyright © 2012–2019, Texas Instruments Incorporated
C28 General-Purpose Input/Output (GPIO)
SYSCLKOUT
SYSCLKOUT
is the period in time of SYSCLKOUT
SYSCLKOUT
× 1 ÷ (2 × GPxCTRL[QUALPRDn])
is the frequency of SYSCLKOUT
SYSCLKOUT
show the calculations that can be used to determine
General-Purpose Input/Output (GPIO)
Table 4-40 and
Figure 4-41.
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