Functional Description and Application Information
MM912F634 - MCU Die Overview
MM912F634
Freescale Semiconductor
163
The system clock can be supplied in several ways enabling a range of system operating frequencies to be supported:
The on-chip frequency locked loop (FLL).
The oscillator.
The clock generated by the FLL or oscillator provides the main system clock frequencies core clock and bus clock. As shown in
Figure 45, these system clocks are used throughout the MCU to drive the core, the memories, and the peripherals.
The Flash memory is supplied by the bus clock which is also being used as a time base to derive the program and erase times
for the NVM.
In order to ensure the presence of the clock the MCU includes an on-chip clock monitor connected to the output of the oscillator.
The clock monitor can be configured to generate a system reset if it is allowed to time out as a result of no oscillator clock being
present.
4.26.6
Modes of Operation
The MCU can operate in different power modes to facilitate power saving when full system performance is not required. These
Some modules feature a software programmable option to freeze the module status whilst the background debug module is
4.26.6.1
Chip Configuration Summary
The different modes and the security state of the MCU affect the debug features (enabled or disabled).
The operating mode out of reset is determined by the state of the MODC signal during reset (see
Table 214). The MODC bit in
the MODE register shows the current operating mode and provides limited mode switching during operation. The state of the
MODC signal is registered into this bit on the rising edge of RESET.
4.26.6.1.1
Normal Single-chip Mode
This mode is intended for normal device operation. The opcode from the on-chip memory is being executed after reset (requires
the reset vector to be programmed correctly).The processor program is executed from internal memory.
4.26.6.1.2
Special Single-chip Mode
This mode is used for debugging single-chip operation, boot-strapping, or security related operations. The background debug
module BDM is active in this mode. The CPU executes a monitor program located in an on-chip ROM. BDM firmware waits for
additional serial commands through the BKGD pin.
4.26.6.2
Power Modes
The MCU features two main low-power modes. Consult the respective module description for module specific behavior in system
stop and system wait mode. An important source of information about the clock system is the Clock and Reset Generator
description (CRG).
Table 214. Chip Modes
Chip Modes
MODC
Normal single chip
1
Special single chip
0