MCF51CN128 Reference Manual, Rev. 6
Freescale Semiconductor
3-1
Chapter 3
Modes of Operation
3.1
Introduction
The operating modes of the MCF51CN128 are described in this chapter. Entry into each mode, exit from
each mode, and functionality while in each of the modes are described.
The overall system mode is generally a function of a number of separate, but inter-related variables: debug
mode, security mode, power mode, and clock mode. Clock modes are discussed in
”
This chapter explores the other dimensions of the system operating mode.
3.2
Features
On the MCF51CN128, wait, stop2, stop3, and stop4 are entered with the CPU STOP instruction. See
, and subsequent sections of this chapter for details.
Table 3-1. MCF51CN128 Mode Features
Mode
Description
Debug
Useful for code development. This device, like all V1 ColdFire devices, debug mode is mutually exclusive
with use of secure mode.
Secure mode BDC access to CPU resources is extremely restricted. It is possible to tell that the device has been
secured, and to clear security, which involves mass erasing the on-chip flash memory. No other CPU
access is allowed. Secure mode can be used in conjunction with each of the power modes below.
Run mode
CPU clocks can be run at full speed and the internal supply is fully regulated.
LPrun mode
CPU and peripheral clocks are restricted to 250 kHz CPU clock and 125 kHz bus clock maximum and the
internal supply is in soft regulation.
Wait mode
CPU shuts down to conserve power; peripheral clocks are running and full regulation is maintained.
LPwait mode
CPU shuts down to conserve power; peripheral clocks are running at reduced speed (125 kHz maximum
bus clock) and the internal voltage regulator is running in loose regulation mode.
Stop modes
System (CPU and peripheral) clocks are stopped.
• Stop4 — All internal circuits are powered (full regulation mode) and internal clock sources still at max
frequency for fastest recovery.
• Stop3 — All internal circuits are loosely regulated and clocks sources are at minimal values (125 kHz
maximum bus clock), providing a good compromise between power utilization and speed of recovery.
• Stop2 — Partial power-down of internal circuits; RAM content is retained. The lowest power mode for
this device. A reset is required to return from stop2 mode.