Z8F6421PM020SC Datasheet, PDF (113/299 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers Z8 Encore-R 64K Series

Z8 Encore!^® 64K Series
Product Specification
93
the Reset and STOP Mode Recovery chapter for more information on STOP Mode
Recovery.
If interrupts are enabled, following completion of the STOP Mode Recovery the eZ8 CPU
responds to the interrupt request by fetching the Watch-Dog Timer interrupt vector and
executing code from the vector address.
WDT Reset in Normal Operation
If configured to generate a Reset when a time-out occurs, the Watch-Dog Timer forces the
device into the Reset state. The WDT status bit in the Watch-Dog Timer Control register is
set to 1. Refer to the Reset and STOP Mode Recovery chapter for more information on
Reset.
WDT Reset in STOP Mode
If enabled in STOP mode and configured to generate a Reset when a time-out occurs and
the device is in STOP mode, the Watch-Dog Timer initiates a STOP Mode Recovery. Both
the WDT status bit and the STOP bit in the Watch-Dog Timer Control register are set to 1
following WDT time-out in STOP mode. Refer to the Reset and STOP Mode Recovery
chapter for more information. Default operation is for the WDT and its RC oscillator to be
enabled during STOP mode.
WDT RC Disable in STOP Mode
To minimize power consumption in STOP Mode, the WDT and its RC oscillator can be
disabled in STOP mode. The following sequence configures the WDT to be disabled when
the 64K Series devices enter STOP Mode following execution of a STOP instruction:
1. Write 55H to the Watch-Dog Timer Control register (WDTCTL).
2. Write AAH to the Watch-Dog Timer Control register (WDTCTL).
3. Write 81H to the Watch-Dog Timer Control register (WDTCTL) to configure the
WDT and its oscillator to be disabled during STOP Mode. Alternatively, write 00H to
the Watch-Dog Timer Control register (WDTCTL) as the third step in this sequence to
reconfigure the WDT and its oscillator to be enabled during STOP Mode.
This sequence only affects WDT operation in STOP mode.
Watch-Dog Timer Reload Unlock Sequence
Writing the unlock sequence to the Watch-Dog Timer (WDTCTL) Control register address
unlocks the three Watch-Dog Timer Reload Byte registers (WDTU, WDTH, and WDTL)
to allow changes to the time-out period. These write operations to the WDTCTL register
address produce no effect on the bits in the WDTCTL register. The locking mechanism
prevents spurious writes to the Reload registers. The follow sequence is required to unlock
the Watch-Dog Timer Reload Byte registers (WDTU, WDTH, and WDTL) for write
access.
PS019915-1005
Watch-Dog Timer