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ACE12022BEM8X View Datasheet(PDF) - Fairchild Semiconductor

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ACE12022BEM8X Datasheet PDF : 39 Pages
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6.0 Timer 0
Timer 0 is a 12-bit free running idle timer. Upon power-up or any
reset, the timer is reset to 0x000 and then counts up continuously
based on the instruction clock of 1MHz (1 µs). Software cannot
read from or write to this timer. However, software can monitor the
timers pending (T0PND) bit that is set every 8192 cycles (initially
4096 cycles after a reset). The T0PND flag is set every other time
the timer overflows (transitions from 0xFFF to 0x000) through a
divide-by-2 circuit. After an overflow, the timer will reset and restart
its counting sequence.
Software can either poll the T0PND bit or vector to an interrupt
subroutine. In order to interrupt on a T0PND, software must be
sure to enable the Timer 0 interrupt enable (T0INTEN) bit in the
Timer 0 control (T0CNTRL) register and also make sure the G bit
is set in SR. Once the timer interrupt is serviced, software should
reset the T0PND bit before exiting the routine. Timer 0 supports
the following functions:
1. Exiting from IDLE mode (See Section 17.0 for details.)
2. Start up delay from HALT mode
3. Watchdog pre-scaler (See Section 7.0 for details.)
The T0INTEN bit is a read/write bit. If set to 0, interrupt requests
from the Timer 0 are ignored. If set to 1, interrupt requests are
accepted. Upon reset, the T0INTEN bit is reset to 0.
The T0PND bit is a read/write bit. If set to 1, it indicates that a Timer
0 interrupt is pending. This bit is set by a Timer 0 overflow and is
Figure 19: Timer 0 Control Register (T0CNTRL)
Bit 7
WKINTEN
Bit 6
x
Bit 5
x
Bit 4
x
reset by software or system reset.
The WKINTEN bit is used in the Multi-input Wakeup/Interrupt
block. See Section 8 for details.
7.0 Watchdog timer
The Watchdog timer is used to reset the device and safely recover
in the rare event of a processor runaway condition.The 12-bit
Timer 0 is used as a pre-scaler for Watchdog timer. The Watchdog
timer must be serviced before every 61,440 cycles but no sooner
than 4096 cycles since the last Watchdog reset. The Watchdog is
serviced through software by writing the value 0x1B to the
Watchdog Service (WDSVR) register (see Figure 20). The part
resets automatically if the Watchdog is serviced too frequent, or
not frequent enough.
The Watchdog timer must be enabled through the Watchdog
enable bit (WDEN) in the initialization register. The WDEN bit can
only be set while the device is in programming mode. Once set, the
Watchdog will always be powered-up enabled. Software cannot
disable the Watchdog. The Watchdog timer can only be disabled
in programming mode by resetting the WDEN bit as long as the
memory write protect (WDIS) feature is not enabled.
WARNING
Ensure that the Watchdog timer has been serviced before enter-
ing IDLE mode because it remains operational during this time.
Bit 3
x
Bit 2
x
Bit 1
T0PND
Bit 0
T0INTEN
Figure 20: Watchdog Server Register (WDSVR)
Bit 7
0
Bit 6
0
Bit 5
0
Bit 4
1
Bit 3
1
Bit 2
0
Bit 1
1
Bit 0
1
24
ACE1202 Product Family Rev. B.1
www.fairchildsemi.com
 

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