C8051F336/7/8/9
software prior to entering the Idle mode if the WDT was initially configured to allow this operation. This pro-
vides the opportunity for additional power savings, allowing the system to remain in the Idle mode indefi-
nitely, waiting for an external stimulus to wake up the system. Refer to Section “18.6. PCA Watchdog Timer
Reset” on page 114 for more information on the use and configuration of the WDT.
17.2. Stop Mode
Setting the Stop Mode Select bit (PCON.1) causes the controller core to enter Stop mode as soon as the
instruction that sets the bit completes execution. In Stop mode the internal oscillator, CPU, and all digital
peripherals are stopped; the state of the external oscillator circuit is not affected. Each analog peripheral
(including the external oscillator circuit) may be shut down individually prior to entering Stop Mode. Stop
mode can only be terminated by an internal or external reset. On reset, the device performs the normal
reset sequence and begins program execution at address 0x0000.
If enabled, the Missing Clock Detector will cause an internal reset and thereby terminate the Stop mode.
The Missing Clock Detector should be disabled if the CPU is to be put to in STOP mode for longer than the
MCD timeout of 100 µs.
17.3. Suspend Mode
Setting the SUSPEND bit (OSCICN.5) causes the hardware to halt the CPU and the high-frequency inter-
nal oscillator, and go into Suspend mode as soon as the instruction that sets the bit completes execution.
All internal registers and memory maintain their original data. Most digital peripherals are not active in Sus-
pend mode. The exception to this is the Port Match feature and Timer 3, when it is run from an external
oscillator source or the internal low-frequency oscillator.
Suspend mode can be terminated by four types of events, a port match (described in Section “20.5. Port
Match” on page 136), a Timer 3 overflow (described in Section “24.3. Timer 3” on page 203), a Comparator
low output (if enabled), or a device reset event. Note that in order to run Timer 3 in Suspend mode, the
timer must be configured to clock from either the external clock source or the internal low-frequency oscil-
lator source. When Suspend mode is terminated, the device will continue execution on the instruction fol-
lowing the one that set the SUSPEND bit. If the wake event (port match or Timer 3 overflow) was
configured to generate an interrupt, the interrupt will be serviced upon waking the device. If Suspend mode
is terminated by an internal or external reset, the CIP-51 performs a normal reset sequence and begins
program execution at address 0x0000.
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