Watchdog Timer
19-4
Élan™SC520 Microcontroller User’s Manual
Each individual write of these keyed sequences is not required to be written back-to-back
as an atomic sequence. Any number of processor cycles, including memory and I/O reads
and writes, can be inserted between the key and the writing of data, as long as they do not
access the Watchdog Timer Control (WDTMRCTL) register.
19.4.1.2
Interrupt Request Generation
To configure interrupt request generation on the watchdog timer, software must set the ENB
bit in the Watchdog Timer Control (WDTMRCTL) register to enable access of the register.
The WRST_ENB bit in this register must be cleared. Once the watchdog timer times out,
the interrupt request is generated.
The watchdog timer interrupt request can be programmed as maskable or non-maskable.
See Chapter 15, “Programmable Interrupt Controller”, for details on selecting a maskable
or non-maskable watchdog timer interrupt request.
If a second time-out event occurs and software has not cleared the IRQ_FLG bit asserted
by the first time-out, the watchdog timer causes a system reset instead of an interrupt
request, regardless of the setting of the WRST_ENB bit.
19.4.1.3
System Reset Generation
To configure the watchdog timer for system reset generation, software must set the ENB
bit to enable access of the register. The WRST_ENB bit must also be set. Once the
watchdog timer times out, the system reset is generated.
19.4.1.4
Time-Out Duration
The Exponent Select (EXP_SEL) bit field in the Watchdog Timer Control (WDTMRCTL)
register indicates the exponent value used to calculate the time-out duration in the following
formula:
Duration = 2
Exponent
/ (33 MHz crystal frequency)
where:
frequency is based on a 33-MHz incoming clock, as shown in Table 19-2.
Notes:
Only the least significant bit set in the EXP_SEL field determines the time-out duration. For example,
setting the field to F0h results in an exponent of 27.
Table 19-2
Watchdog Timer Time-Out Duration
EXP_SEL Field
Exponent
33.000 MHz
33.333 MHz
00h
invalid value
infinity
infinity
01h
14
496
µ
s
492
µ
s
02h
24
508 ms
503 ms
04h
25
1.02 s
1.01 s
08h
26
2.03 s
2.01 s
10h
27
4.07 s
4.03 s
20h
28
8.13 s
8.05 s
40h
29
16.27 s
16.11 s
80h
30
32.54 s
32.21 s
Содержание Elan SC520
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Страница 42: ...Architectural Overview 1 14 lan SC520 Microcontroller User s Manual...
Страница 78: ...System Initialization 3 22 lan SC520 Microcontroller User s Manual...
Страница 108: ...Clock Generation and Control 5 10 lan SC520 Microcontroller User s Manual...
Страница 118: ...Reset Generation 6 10 lan SC520 Microcontroller User s Manual...
Страница 148: ...System Arbitration 8 24 lan SC520 Microcontroller User s Manual...
Страница 214: ...SDRAM Controller 10 36 lan SC520 Microcontroller User s Manual...
Страница 230: ...Write Buffer and Read Buffer 11 16 lan SC520 Microcontroller User s Manual...
Страница 288: ...GP Bus DMA Controller 14 22 lan SC520 Microcontroller User s Manual...
Страница 316: ...Programmable Interval Timer 16 8 lan SC520 Microcontroller User s Manual...
Страница 328: ...Software Timer 18 4 lan SC520 Microcontroller User s Manual...
Страница 346: ...Real Time Clock 20 12 lan SC520 Microcontroller User s Manual...
Страница 360: ...UART Serial Ports 21 14 lan SC520 Microcontroller User s Manual...
Страница 414: ...AMDebug Technology 26 8 lan SC520 Microcontroller User s Manual...