SPRS439M – JUNE 2007 – REVISED AUGUST 2012
The user can select the type of input qualification for each GPIO pin via the GPxQSEL1/2 registers from
four choices:
• Synchronization To SYSCLKOUT Only (GPxQSEL1/2 = 0, 0): This is the default mode of all GPIO pins
at reset and it simply synchronizes the input signal to the system clock (SYSCLKOUT).
• Qualification Using Sampling Window (GPxQSEL1/2 = 0, 1 and 1, 0): In this mode the input signal,
after synchronization to the system clock (SYSCLKOUT), is qualified by a specified number of cycles
before the input is allowed to change.
Time Between Samples
GPyCTRL Reg
GPIOx
SYNC
Qualification
Input Signal
Qualified by
3 or 6 Samples
GPxQSEL
SYSCLKOUT
Number of Samples
Figure 4-19. Qualification Using Sampling Window
•
The sampling period is specified by the QUALPRD bits in the GPxCTRL register and is configurable in
groups of 8 signals. It specifies a multiple of SYSCLKOUT cycles for sampling the input signal. The
sampling window is either 3-samples or 6-samples wide and the output is only changed when ALL
samples are the same (all 0s or all 1s) as shown in
(for 6-sample mode).
No Synchronization (GPxQSEL1/2 = 1,1): This mode is used for peripherals where synchronization is
not required (synchronization is performed within the peripheral).
•
Due to the multi-level multiplexing that is required on the device, there may be cases where a peripheral
input signal can be mapped to more then one GPIO pin. Also, when an input signal is not selected, the
input signal will default to either a 0 or 1 state, depending on the peripheral.
Copyright © 2007–2012, Texas Instruments Incorporated
Peripherals
105
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