![Infineon Technologies XC2200 User Manual Download Page 473](http://html1.mh-extra.com/html/infineon-technologies/xc2200/xc2200_user-manual_2055439473.webp)
XC2200 Derivatives
System Units (Vol. 1 of 2)
System Control Unit (SCU)
User’s Manual
6-213
V2.1, 2008-08
SCU, V1.13
•
Timer is reloaded with FFFF
H
Disable Mode
Disable Mode is provided for applications that do not require the Watchdog Timer
function. Disable Mode is entered when instruction DISWDT is executed, either before
End-of-Init, if CPUCON1.WDTCTL = 0, or at any time, if CPUCON1.WDTCTL = 1.
The timer is reloaded with the value of WDTREL.RELV when Disable Mode is entered.
A transition from Disable Mode to Normal Mode is performed when instruction ENWDT
is executed while CPUCON1.WDTCTL = 1.
Prewarning Mode
Prewarning Mode is entered always when a Watchdog error is detected. This is an
overflow in Normal Mode. Instead of immediately requesting a reset of the device, the
WDT enables the system to enter a secure state by issuing the prewarning output before
the reset occurs. Receiving the prewarning, the CPU and the system are requested to
finish all pending transaction requests and to not generate new ones. The prewarning is
signalled via an interrupt. The CPU can recognize the WDT prewarning interrupt via
register INTSTAT. After finishing all pending transactions, the CPU should execute the
IDLE instruction to stop all further processing before the coming reset.
In Prewarning Mode, the WDT starts counting from FFFF
H
upwards, and then requests
a WDT reset on the overflow of the WDT from FFFF
H
to 0000
H
. A reset request of the
.WDT can not be avoided. No reset will be requested If
RSTCON1.WDT is cleared. The WDT does not react anymore to accesses to its
registers and to the ENWDT or DISWDT instruction, nor will it change its state until it is
reset.
A further feature of the WDT detects double errors and sets the whole system into a
permanent WDT reset. This feature prevents the XC2200 from executing random wrong
code for longer than the occurence of the overflow, and prevents the XC2200 from being
repeatedly reset by the WDT.
Double WDT Reset
If the Watchdog induced reset (Application or Internal Application Reset) occurs twice
back-to-back, a severe system malfunction is assumed and the XC2200 is held in a reset
of the type as configured in
.WDT (or just not) until a Power-on Reset occurs.
This prevents the device from being periodically reset if, for instance, connection to the
external memory has been lost such that even system initialization could not be
performed.
Note: Triggering a PORST upon a WDT reset will never result in a double WDT overflow.
If the WDT is configured by RSTCON1.WDT to request an Application Reset or an
Internal Application Reset the second reset request will be permanently asserted