Chapter 5 External Bus Interface (S12XEBIV4)
MC9S12XE-Family Reference Manual , Rev. 1.19
256
Freescale Semiconductor
5.4.6
Low-Power Options
The XEBI does not support any user-controlled options for reducing power consumption.
5.4.6.1
Run Mode
The XEBI does not support any options for reducing power in run mode.
Power consumption is reduced in single-chip modes due to the absence of the external bus interface.
Operation in expanded modes results in a higher power consumption, however any unnecessary toggling
of external bus signals is reduced to the lowest indispensable activity by holding the previous states
between external accesses.
5.4.6.2
Wait Mode
The XEBI does not support any options for reducing power in wait mode.
5.4.6.3
Stop Mode
The XEBI will cease to function in stop mode.
5.5
Initialization/Application Information
This section describes the external bus interface usage and timing. Typical customer operating modes are
normal expanded mode and emulation modes, specifically to be used in emulator applications. Taking the
availability of the external wait feature into account the use cases are divided into four scenarios:
•
Normal expanded mode
— External wait feature disabled
–
External wait feature enabled
•
Emulation modes
–
Emulation single-chip mode (without wait states)
–
Emulation expanded mode (with optional access stretching)
Normal single-chip mode and special single-chip mode do not have an external bus. Special test mode is
used for factory test only. Therefore, these modes are omitted here.
All timing diagrams referred to throughout this section are available in the Electrical Characteristics
appendix of the SoC section.
5.5.1
Normal Expanded Mode
This mode allows interfacing to external memories or peripherals which are available in the commercial
market. In these applications the normal bus operation requires a minimum of 1 cycle stretch for each
external access.
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages