MC9S12XD256MAL Datasheet, PDF (71/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

1.5 Modes of Operation
Chapter 1 Device Overview MC9S12XD-Family
1.5.1 User Modes
1.5.1.1 Normal Expanded Mode
Ports K, A, and B are configured as a 23-bit address bus, ports C and D are configured as a 16-bit data bus,
and port E provides bus control and status signals. This mode allows 16-bit external memory and
peripheral devices to be interfaced to the system. The fastest external bus rate is divide by 2 from the
internal bus rate.
1.5.1.2 Normal Single-Chip Mode
There is no external bus in this mode. The processor program is executed from internal memory. Ports A,
B,C,D, K, and most pins of port E are available as general-purpose I/O.
1.5.1.3 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 is waiting for additional serial commands through the BKGD pin. There
is no external bus after reset in this mode.
1.5.1.4 Emulation of Expanded Mode
Developers use this mode for emulation systems in which the users target application is normal expanded
mode. Code is executed from external memory or from internal memory depending on the state of
ROMON and EROMON bit. In this mode the internal operation is visible on external bus interface.
1.5.1.5 Emulation of Single-Chip Mode
Developers use this mode for emulation systems in which the user’s target application is normal
single-chip mode. Code is executed from external memory or from internal memory depending on the state
of ROMON and EROMON bit. In this mode the internal operation is visible on external bus interface.
1.5.1.6 Special Test Mode
Freescale internal use only.
1.5.2 Low-Power Modes
The microcontroller features two main low-power modes. Consult the respective sections for information
on the module behavior in system stop, system pseudo stop, and system wait mode. An important source
of information about the clock system is the Clock and Reset Generator S12CRG section.
MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor
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