S912XEG384J3VA Datasheet, PDF (76/1324 Pages) Freescale Semiconductor, Inc – MC9S12XEP100 Reference Manual Covers MC9S12XE Family

Chapter 1 Device Overview MC9S12XE-Family
The program Flash memory and the EEPROM are supplied by the bus clock and the oscillator clock. The
oscillator clock is used as a time base to derive the program and erase times for the NVM’s.
The CAN modules may be configured to have their clock sources derived either from the bus clock or
directly from the oscillator clock. This allows the user to select its clock based on the required jitter
performance.
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 invoke the PLL self-clocking mode or to
generate a system reset if it is allowed to time out as a result of no oscillator clock being present.
In addition to the clock monitor, the MCU also provides a clock quality checker which performs a more
accurate check of the clock. The clock quality checker counts a predetermined number of clock edges
within a defined time window to insure that the clock is running. The checker can be invoked following
specific events such as on wake-up or clock monitor failure.
1.4 Modes of Operation
The MCU can operate in different modes associated with MCU resource mapping and bus interface
configuration. These are described in 1.4.1 Chip Configuration Summary.
The MCU can operate in different power modes to facilitate power saving when full system performance
is not required. These are described in 1.4.2 Power Modes.
Some modules feature a software programmable option to freeze the module status whilst the background
debug module is active to facilitate debugging. This is described in 1.4.3 Freeze Mode.
For system integrity support separate system states are featured as explained in 1.4.4 System States.
1.4.1 Chip Configuration Summary
The MCU can operate in six different modes associated with resource configuration. The different modes,
the state of ROMCTL and EROMCTL signal on rising edge of RESET and the security state of the MCU
affect the following device characteristics:
• External bus interface configuration
• Flash in memory map, or not
• Debug features enabled or disabled
The operating mode out of reset is determined by the states of the MODC, MODB, and MODA signals
during reset (see Table 1-12). The MODC, MODB, and MODA bits in the MODE register show the current
operating mode and provide limited mode switching during operation. The states of the MODC, MODB,
and MODA signals are latched into these bits on the rising edge of RESET.
In normal expanded mode and in emulation modes the ROMON bit and the EROMON bit in the
MMCCTL1 register defines if the on chip flash memory is the memory map, or not. (See Table 1-12.) For
a detailed explanation of the ROMON and EROMON bits refer to the MMC description.
MC9S12XE-Family Reference Manual Rev. 1.25
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Freescale Semiconductor