Modes of Operation
MCF51CN128 Reference Manual, Rev. 6
3-8
Freescale Semiconductor
3.7
Wait Modes
3.7.1
Wait Mode
Wait mode is entered by executing a STOP instruction after configuring the device as shown in
After execution of the STOP instruction, the CPU enters a low-power state in which it is not clocked.
The V1 ColdFire core does not differentiate between stop and wait modes. Both are stop from the core’s
perspective. The difference between the two is at the device level. In stop mode, most peripheral clocks
are shut down. In wait mode, they continue to run.
XCSR[ENBDM] must be set prior to entering wait mode if the device is required to respond to BDM
commands while in wait.
In all cases when BDM is in use, or must be available, the BKGD/MS function must be enabled by clearing
the PTDPF1[D6] bit. See
Section 9.7, “Pin Mux Controls
,” for additional details.
When an interrupt request occurs, the CPU exits wait mode and resumes with exception processing,
beginning with the stacking operations leading to the interrupt service routine.
3.7.2
Low-Power Wait Mode (LPwait)
Low-power wait mode is entered by executing a STOP instruction while the MCU is in low-power run
mode and configured as shown in
. In the low-power wait mode, the on-chip voltage regulator
remains in its standby state, the power consumption is reduced to a minimum that allows most modules to
maintain funtionality. To reduce the power consumption further, disable the clocks to all unused
peripherals by clearing the corresponding bits in the SCGC registers.
Low-power run mode restrictions also apply to low-power wait mode.
If SPMSC2[LPWUI] is set when the STOP instruction is executed, the voltage regulator returns to full
regulation when wait mode is exited. The MCG FLLs can be set for full speed immediately in the interrupt
service routine.
If SPMSC2[LPWUI] is cleared when the STOP instruction is executed, the device returns to low-power
run mode.
Any reset exits low-power wait mode, clears SPMSC2[LPR], and returns the device to normal run mode.
3.7.2.1
BDM in Low-Power Wait Mode
If a device is in low-power wait mode, a falling edge on an active BKGD/MS pin exits low-power wait
mode, clears the LPR and LPRS bits in SPMSC2, and returns the device to normal run mode.