C8051F360/1/2/3/4/5/6/7/8/9
9.5.1. Idle Mode
Setting the Idle Mode Select bit (PCON.0) causes the CIP-51 to halt the CPU and enter Idle mode as soon
as the instruction that sets the bit completes. All internal registers and memory maintain their original
data. All analog and digital peripherals can remain active during Idle mode.
Idle mode is terminated when an enabled interrupt or RST is asserted. The assertion of an enabled inter-
rupt will cause the Idle Mode Selection bit (PCON.0) to be cleared and the CPU to resume operation. The
pending interrupt will be serviced and the next instruction to be executed after the return from interrupt
(RETI) will be the instruction immediately following the one that set the Idle Mode Select bit. If Idle mode is
terminated by an internal or external reset, the CIP-51 performs a normal reset sequence and begins pro-
gram execution at address 0x0000.
If enabled, the WDT will eventually cause an internal watchdog reset and thereby terminate the Idle mode.
This feature protects the system from an unintended permanent shutdown in the event of an inadvertent
write to the PCON register. If this behavior is not desired, the WDT may be disabled by software prior to
entering the Idle mode if the WDT was initially configured to allow this operation. This provides the oppor-
tunity for additional power savings, allowing the system to remain in the Idle mode indefinitely, waiting for
an external stimulus to wake up the system. Refer to Section 22.3 for more information on the use and
configuration of the WDT.
Note: Any instruction which sets the IDLE bit should be immediately followed by an instruction which has
two or more opcode bytes. For example:
// in ‘C’:
PCON |= 0x01;
PCON = PCON;
; in assembly:
ORL PCON, #01h
MOV PCON, PCON
// Set IDLE bit
// ... Followed by a 3-cycle Dummy Instruction
; Set IDLE bit
; ... Followed by a 3-cycle Dummy Instruction
If the instruction following the write to the IDLE bit is a single-byte instruction and an interrupt occurs during
the execution of the instruction of the instruction which sets the IDLE bit, the CPU may not wake from IDLE
mode when a future interrupt occurs.
9.5.2. Stop Mode
Setting the Stop Mode Select bit (PCON.1) causes the CIP-51 to enter Stop mode as soon as the instruc-
tion that sets the bit completes. In Stop mode, the CPU and oscillators are stopped, effectively shutting
down all digital peripherals. Each analog peripheral must be shut down individually prior to entering Stop
Mode. Stop mode can only be terminated by an internal or external reset. On reset, the CIP-51 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 sleep for longer than the MCD
timeout of 100 µs.
9.5.3. Suspend Mode
The C8051F36x devices feature a low-power SUSPEND mode, which stops the internal oscillator until an
awakening event occurs. See Section “16.1.1. Internal Oscillator Suspend Mode” on page 170.
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SILABS [ SILICON LABORATORIES ]
