Watchdog Timer
Am186™CC/CH/CU Microcontrollers User’s Manual
11-5
11.5.4
Software-Related Considerations
■
Even if the watchdog-timer default configuration is appropriate for the application,
software should always perform an enabling write to the watchdog timer. This write
causes most of the fields of the WDTCON register to become read-only, preventing run-
away code from disabling or otherwise modifying the watchdog timer behavior.
■
If a watchdog-timer time-out occurs when the timer is programmed with WRST cleared,
an NMI is generated, the time-out counter is reset, and the NMIFLAG bit is set. If the
NMIFLAG bit is not cleared before a second watchdog timer time-out, a reset is generated
regardless of the setting of WRST.
■
The watchdog timer can generate a nonmaskable interrupt (NMI). This interrupt can be
taken at any time. Unlike the maskable interrupts, the controller is not inhibited from
taking a second NMI request while the NMI ISR is executing. Therefore, a watchdog
timer NMI can interrupt, or be interrupted by, an externally generated NMI.
11.5.5
Comparison to Other Devices
The watchdog timer is based on the watchdog timer in the Am186ES and Am186ED
microcontrollers, with the following enhancements:
■
Multiple writes are allowed to the WDTCON control register following reset as long as
these writes have the enable bit cleared. When a write is detected with the enable bit
set, the control register becomes read-only except for the NMI Flag (NMIFLAG) bit and
the Reset Flag (RSTFLAG) bit.
■
The time-out counter is automatically reset by a write that enables the watchdog timer.
■
A read to the WDTCON register does not clear the NMIFLAG or RSTFLAG bits. Software
must write a 0 value to each of these bits to clear them. Writing a 1 to these bit positions
has no effect.
■
The watchdog timer can generate an external signal when a watchdog-timer reset event
occurs.
11.6
INITIALIZATION
At reset, the following occurs:
■
After an external reset, the watchdog timer is enabled and programmed to generate a
reset including generation of the RESOUT signal on time-out, the RSTFLAG bit is
cleared, and the time-out value is 2
26
clock cycles.
■
After a watchdog-timer reset, the watchdog timer is enabled and programmed to
generate a reset on the time-out, the RSTFLAG bit is set, and the time-out value is 2
26
clock cycles. The EXRST bit, which determines whether RESOUT is asserted for
watchdog timer resets, retains its previously programmed value.
■
A watchdog-timer reset affects the microcontroller the same as an external reset, except
for the following:
– Pinstraps are not sampled.
– The RESCON register is not reset.
– The RSTFLAG bit is cleared by an external reset, and set in an internal reset.
– The EXRST bit is set by an external reset, and unchanged by an internal reset.
Summary of Contents for Am186 CC
Page 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Page 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Page 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Page 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Page 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Page 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Page 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Page 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Page 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...