N2HET Functional Description
820
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
High-End Timer (N2HET) Module
Table 20-10. N2HET Pin Disable Feature
HETPINDIS.x
nDIS Pin (Input)
HET_PIN_ENA (HETGCR.24)
HETDIR.x
Output Buffer
0
X
X
0
Disabled
0
X
X
1
Enabled
1
0
X
0
Disabled
1
0
X
1
Disabled
1
1
X
0
Disabled
1
1
0
1
Disabled
1
1
1
1
Enabled
An interrupt capable device I/O pin can share the same pin as the N2HET nDIS signal. Normally GIOA[5]
serves as nDIS for N2HET1 and GIOB[2] as nDIS for N2HET2. Check the device datasheet for the actual
implementation. Sharing a pin with a GIO pin that is Interrupt capable allows the N2HET nDIS input to
also generate an interrupt to the CPU. An active low level on nDIS is intended to signal an abnormal
situation as described above. All N2HET pins, which are selected with the N2HET Pin Disable Register
(HETPINDIS), will be put in the high-impedance state by hardware immediately after the nDIS signal is
pulled low. At this time a CPU interrupt is issued, if it is enabled in the GIO pin logic.
The bit HET_PIN_ENA is automatically cleared in the failure condition and this state remains as long as
the software explicitly sets the bit again. The steps to do this are:
•
Software detects, by reading the HETDIN register of the GIO pin, that the level on nDIS is inactive
(high).
•
Software sets bit HET_PIN_ENA to deactivate the high impedance state of the pins.
20.2.6 Suppression Filters
Each N2HET pin is equipped with a suppression filter. If the pin is configured as an input it enables to filter
out pulses shorter than a programmable duration. Each filter consists of a 10-bit down counter, which
starts counting at a programmable preloaded value and is decremented using the VCLK2 clock.
•
The counter starts counting when the filter input signal has the opposite state of the filter output signal.
The output signal is preset to the same input signal state after reset, in order to ensure proper
operation after device reset.
•
Once the counter reaches zero without detecting an opposite pin state on the filter input signal, the
output signal is set to the opposite state.
•
When the counter detects an opposite pin action on the filter input signal before reaching zero, the
counter is loaded with it's preload value and the opposite pin action on the filter output signal does not
take place. The counter resumes at the preload value until it detects an opposite pin action on the
input signal again.
•
Therefore the filter output signal is delayed compared to the filter input signal. The amount of delay
depends on the counter clock frequency (VCLK2) and the programmed preload value.
•
The accuracy of the output signal is +/- the counter clock frequency.
gives examples for a 100 MHz VCLK2 frequency.