HT46R232/HT46C232
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Watchdog Timer
the interrupt is enabled and the stack is not full, the regu-
lar interrupt response takes place. When an interrupt re-
quest flag is set to ²1² before entering the HALT mode,
the wake-up function of the related interrupt will be dis-
abled. If wake-up event occurs, it takes 1024 fSYS (sys-
tem clock period) to resume normal operation. In other
words, a dummy period is inserted after wake-up. If the
wake-up results from an interrupt acknowledgment, the
actual interrupt subroutine execution is delayed by more
than one cycle. However, if the wake-up results in the
next instruction execution, this will be executed per-
formed immediately after the dummy period is finished.
CLRWDT times equal one), any execution of the CLR
WDT instruction will clear the WDT. In case ²CLR
WDT1² and ²CLR WDT2² are chosen (i.e. CLRWDT
times equal two), these two instructions must be exe-
cuted to clear the WDT; otherwise, the WDT may reset
the chip because of time-out.
If the WDT time-out period is selected fs/212 (option), the
WDT time-out period ranges from fs/212~fs/213, since the
²CLR WDT² or ²CLR WDT1² and ²CLR WDT2²
instructions only clear the last two stages of the WDT.
Power Down Operation - HALT
To minimize power consumption, all the I/O pins should
be carefully managed before entering the HALT status.
The HALT mode is initialized by the ²HALT² instruction
and results in the following...
Reset
·
The system oscillator turned off but the WDT oscillator
keeps running (if the WDT oscillator or the real time
clock is selected).
There are three ways in which a reset may occur:
·
·
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RES reset during normal operation
RES reset during HALT
·
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The contents of the on-chip RAM and registers remain
unchanged
WDT time-out reset during normal operation
The WDT will be cleared and start recounting (if the
WDT clock source is from the WDT oscillator or the
real time clock)
The WDT time-out during HALT differs from other chip
reset conditions, for it can perform a ²warm reset² that
resets only the program counter and SP, leaves the
other circuits at their original state. Some registers re-
main unaffected during any other reset conditions. Most
registers are reset to the ²initial condition² when the re-
set conditions are met. Examining the PDF and TO
flags, the program can distinguish between different
²chip resets².
·
·
All of the I/O ports maintain their original status
The PDF flag is set and the TO flag is cleared
The system quits the HALT mode by an external reset,
an interrupt, an external falling edge signal on port Aor a
WDT overflow. An external reset causes a device initial-
ization and the WDT overflow performs a ²warm reset².
After examining the TO and PDF flags, the reason for
chip reset can be determined. The PDF flag is cleared
by system power-up or by executing the ²CLR WDT² in-
struction and is set when executing the ²HALT² instruc-
tion. On the other hand, the TO flag is set if the WDT
time-out occurs, and causes a wake-up that only resets
the program counter and SP; and leaves the others in
their original status.
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The port A wake-up and interrupt methods can be con-
sidered as a continuation of normal execution. Each bit
in port A can be independently selected to wake up the
device by the option. Awakening from an I/O port stimu-
lus, the program will resume execution of the next in-
struction. If it is awakening from an interrupt, two
sequences may occur. If the related interrupt is disabled
or the interrupt is enabled but the stack is full, the pro-
gram will resume execution at the next instruction. But if
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Reset Circuit
Note: Most applications can use the Basic Reset Cir-
cuit as shown, however for applications with
extensive noise, it is recommended to use the
Hi-noise Reset Circuit.
Rev. 1.50
12
January 21, 2009
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
