Power-Down Mode
5-36
5.8
Power-Down Mode
The ’C2xx has a power-down mode that allows the ’C2xx core to enter a dor-
mant state and use less power than during normal operation. Executing an
IDLE instruction initiates power-down mode. When the IDLE instruction
executes, the program counter is incremented once, and then all CPU activi-
ties are halted. While the ’C2xx is in power-down mode, all of its internal con-
tents are maintained. The content of all on-chip RAM remains unchanged. The
peripheral circuits continue to operate, allowing the serial ports and the timer
to take the CPU out of the power-down state. The CLKOUT1 pin remains ac-
tive if bit 0 of the CLK register is set to 0.
The methods for terminating power-down mode depend on whether the pow-
er-down was initiated under normal circumstances or as part of a HOLD opera-
tion. The following subsections describe the differences.
5.8.1
Normal Termination of Power-Down Mode
If power-down has been initiated, any hardware interrupt (internal or external)
takes the processor out of the IDLE state. If you use reset or NMI, the CPU will
immediately execute the corresponding interrupt service routine. In addition,
if you use reset, registers will assume their reset values.
For a maskable hardware interrupt to wake the processor, it must be un-
masked by the interrupt mask register (IMR bit = 1). However, if the interrupt
is unmasked and is then requested, the processor will leave the IDLE state re-
gardless of the value of the INTM bit (bit 9 of status register ST0). The value
of the INTM bit will only determine the action of the CPU
after power-down has
been terminated:
-
INTM = 0. The interrupt is enabled, and the CPU executes the correspond-
ing interrupt service routine.
-
INTM = 1. The interrupt is disabled, and the CPU continues with the
instruction after IDLE.
If you do not want the CPU to follow an interrupt service routine before continu-
ing with the interrupted program sequence:
-
Do not use reset or NMI to bring the processor out of power-down.
-
Make sure your program globally disables maskable interrupts (sets INTM
to 1) before IDLE is executed.
