TMS320VC5441_17 Datasheet, PDF (49/91 Pages) Texas Instruments – Fixed-Point Digital Signal Processor

Functional Overview
The registers WDTIM, WDPRD, WDTCR, and the PREMD bit in WDTSCR must be configured before the
watchdog enters the active state. By default, WDTIM =FFFFh, WDPRD = FFFFh, PREMD = 1, TDDR = 1111b.
Writing a ‘1’ to WDEN and configuring the PREMD bit must be done at the same time that A7Eh is written to
WDKEY in watchdog pre-active state.
3.2.5.6 Watchdog State Diagram
Figure 3−25 shows the watchdog operation state diagram.
Power Up/
Reset
(Hardware)
Not 5C6h to
WDKEY
5C6h to
WDKEY
A7Eh to
WDKEY
Initial State
(Watchdog
Disabled)
(WDTIM=FFFFh)
(WDPRD=FFFFh)
(TDDR=1111b)
(PREMD=1)
5C6h to WDKEY
Pre-Active
State
A7Eh to WDKEY
with ”1” to WDEN
(Reload Timer,
Clear WDFLAG,
Enable Output Pin)
Active State
(Waiting for
5C6h)
Not A7Eh or 5C6h
to WDKEY
Timeout
State
(Watchdog
Disabled)
(Output Pin
Disconnected)
Not 5C6h or A7Eh
to WDKEY
Output Pin Asserted
WDFLAG Set
WD INT Triggered
Timeout!
Output Pin Asserted
WDFLAG Set
WD INT Triggered
Timeout!
Output Pin Asserted
WDFLAG Set
WD INT Triggered
Not A7Eh or 5C6h
to WDKEY
Output Pin Asserted
WDFLAG Set
WD INT Triggered
5C6h to
WDKEY
A7Eh to
WDKEY
(Register
Reload)
Service
State
(Waiting for
A7Eh)
Figure 3−25. Watchdog Operation State Diagram
5C6h to
WDKEY
As shown in Figure 3−25, the watchdog is disabled before it enters the active state. Even though disabled,
the WD interrupt (WD_TINT) may be triggered periodically although the watchdog output pin (x_WTOUT) will
not be asserted. The interrupt may be utilized to:
• Indicate that watchdog is not in active state
• Allow the watchdog timer to act as a general-purpose time counter if the watchdog functionality is not
needed.
3.2.5.7 Watchdog Register Write Protection
Once the watchdog is enabled, writes to registers WDTIM, WDPRD, and WDTCR will have no effect. Writes
to the WDFLAG, WDEN, and PREMD bits in register WDTSCR will have no effect. However, writing an
incorrect key (not 5C6h or A7Eh) to WDKEY will result in an immediate time-out.
December 1999 − Revised October 2008
SPRS122F
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