PXS20RM Datasheet, PDF (708/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Flexible Motor Control Pulse Width Modulator Module (FlexPWM)
FFLAG - Fault Flags
These read-only flag is set within two CPU cycles after a transition to active on the FAULTx pin. Clear
FFLAGx by writing a logic one to it. A reset clears FFLAG.
1 = Fault on the FAULTx pin.
0 = No fault on the FAULTx pin.
25.4.5.3 Fault Filter Register (FFILT)
PWM_BASE
+$150
0
1
Read
Write
GST ⁰
R
Reset
00
2 3 4 5 6 7 8 9 10 11 12 13 14 15
000
FILT_CNT
FILT_PER
00000000000000
Figure 25-66. Fault Filter Register (FFILT)
The settings in this register are shared among each of the fault input filters.
GSTR - Fault Glitch Stretch Enable
This bit is used to enable the fault glitch stretching logic. This logic ensures that narrow fault glitches
are stretched to be at least 2 IPBus clock cycles wide. In some cases a narrow fault input can cause
problems due to the short PWM output shutdown/re-activation time. The stretching logic ensures that
a glitch on the fault input, when the fault filter is disabled, will be registered in the fault flags.
1 = Input fault signals will be stretched to at least 2 IPBus clock cycles.
0 = Fault input glitch stretching is disabled.
FILT_CNT - Fault Filter Count
These bits represent the number of consecutive samples that must agree prior to the input filter
accepting an input transition. A value of 0 represents 3 samples. A value of 7 represents 10 samples.
The value of FILT_CNT affects the input latency as described in Section 25.4.5.3.1, Input Filter
Considerations.
FILT_PER - Fault Filter Period
These bits represent the sampling period (in IPBus clock cycles) of the fault pin input filter. Each input
is sampled multiple times at the rate specified by FILT_PER. If FILT_PER is 0x00 (default), then the
input filter is bypassed. The value of FILT_PER affects the input latency as described in
Section 25.4.5.3.1, Input Filter Considerations.
25.4.5.3.1 Input Filter Considerations
The FILT_PER value should be set such that the sampling period is larger than the period of the expected
noise. This way a noise spike will only corrupt one sample. The FILT_CNT value should be chosen to
reduce the probability of noisy samples causing an incorrect transition to be recognized. The probability
of an incorrect transition is defined as the probability of an incorrect sample raised to the FILT_CNT+3
power.
25-62
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor