Chapter 26 eTimer
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
731
26.6.2.17 Input filter considerations
The FILT_PER value should be set such that the sampling period is larger 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 FI 3 power.
The values of FILT_PER and FILT_CNT must also be traded off against the desire for minimal latency in
recognizing input transitions. Turning on the input filter (setting FILT_PER to a non-zero value) introduces
a latency of:
{
[
(FI 3) × FILT_PER
]
+ 2
}
IPBus clock periods.
26.6.3
Watchdog timer registers
The base address of the Watchdog Timer registers is equal to the base address of the eTimer plus an offset
of 0x100.
26.6.3.1
Watchdog Time-Out registers (WDTOL and WDTOH)
Address: Base + 0x0100
Access: User read/write
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
R
WDTOL
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Figure 26-19. Watchdog Time-out Low Word register (WDTOL)
Address: Base + 0x0102
Access: User read/write
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
R
WDTOH
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Figure 26-20. Watchdog Time-Out High Word register (WDTOH)
Table 26-19. WDTOL, WDTOH field descriptions
Field
Description
WDTO
Watchdog Time-out
Note:
These registers are combined to form the 32-bit time-out count for the Timer watchdog
function. This time-out count is used to monitor for inactivity on the inputs when channel 0 is
in the quadrature decode count mode. The watchdog function is enabled whenever WDTO
contains a non-zero value (although actual counting only occurs if channel 0 is in quadrature
decode counting mode). The watchdog time-out down counter is loaded whenever WDTOH
is written. These registers are not byte accessible. See
Section 26.7.3.5, “Watchdog timer
for
more information on the use of the watchdog timer.
