counter continues to increment. If the 5-bit counter overflows, that is, the counter exceeds
the value of the FFVAL[3:0] bits, the new fault input n value is validated. It is then
transmitted as a pulse edge to the edge detector.
If the opposite edge appears on the fault input n signal before validation (counter
overflow), the counter is reset. At the next input transition, the counter starts counting
again. Any pulse that is shorter than the minimum value selected by FFVAL[3:0] bits (×
system clock) is regarded as a glitch and is not passed on to the edge detector.
The fault input n filter is disabled when the FFVAL[3:0] bits are zero or when
FAULTnEN = 0. In this case, the fault input n signal is delayed 2 rising edges of the
system clock and the FAULTFn bit is set on 3th rising edge of the system clock after a
rising edge occurs on the fault input n.
If FFVAL[3:0] ≠ 0000 and FAULTnEN = 1, then the fault input n signal is delayed (3 +
FFVAL[3:0]) rising edges of the system clock, that is, the FAULTFn bit is set (4 +
FFVAL[3:0]) rising edges of the system clock after a rising edge occurs on the fault input
n.
fault input n*
system clock
* where n = 3, 2, 1, 0
synchronizer
fault input n* value
FAULTFn*
0000)
and (FFLTRnEN*)
0
1
rising edge
detector
fault input
polarity
control
Fault filter
(5-bit counter)
CLK
CLK
D
D
Q
Q
FLTnPOL
(FFVAL[3:0]
Figure 38-234. Fault input n control block diagram
If the fault control and fault input n are enabled and a rising edge at the fault input n
signal is detected, a fault condition has occurred and the FAULTFn bit is set. The
FAULTF bit is the logic OR of FAULTFn[3:0] bits. See the following figure.
fault interrupt
FAULTIE
FAULTIN
fault input 0 value
fault input 1 value
fault input 2 value
fault input 3 value
FAULTF
FAULTF0
FAULTF1
FAULTF2
FAULTF3
Figure 38-235. FAULTF and FAULTIN bits and fault interrupt
Chapter 38 FlexTimer Module (FTM)
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
Freescale Semiconductor, Inc.
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