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
SYSCLKOUT
If, for example, f
SYSCLKOUT
= 60 MHz
then the signal will be sampled at 60 MHz or one sample every 16.67 ns.
Example: Minimum Sampling Frequency:
If GPxCTRL[QUALPRDn] = 0xFF (255)
then the sampling frequency is f
SYSCLKOUT
× 1 ÷ (2 × GPxCTRL[QUALPRDn])
If, for example, f
SYSCLKOUT
= 60 MHz
then the signal will be sampled at 60 MHz × 1 ÷ (2 × 255) or one sample every 8.5 μs.
Number of samples:
The number of times the signal is sampled is either 3 samples or 6 samples as specified in the qualification
selection (GPAQSEL1, GPAQSEL2, GPBQSEL1, and GPBQSEL2) registers. When 3 or 6 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
. Likewise, for a six-sample window, the sampling window width is 5 sampling periods wide.
show the calculations that can be used to determine the total sampling window width
based on GPxCTRL[QUALPRDn] and the number of samples taken.
Table 1-61. Case 1: Three-Sample Sampling Window Width
Total Sampling Window Width
If GPxCTRL[QUALPRDn] = 0
2 × T
SYSCLKOUT
If GPxCTRL[QUALPRDn] ≠ 0
2 × 2 × GPxCTRL[QUALPRDn] × T
SYSCLKOUT
Where T
SYSCLKOUT
is the period in time of SYSCLKOUT
Table 1-62. Case 2: Six-Sample Sampling Window Width
Total Sampling Window Width
If GPxCTRL[QUALPRDn] = 0
5 × T
SYSCLKOUT
If GPxCTRL[QUALPRDn] ≠ 0
5 × 2 × GPxCTRL[QUALPRDn] × T
SYSCLKOUT
Where T
SYSCLKOUT
is the period in time of SYSCLKOUT
System Control and Interrupts
118
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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