Chapter 3 Memory Mapping Control (S12XMMCV4)
MC9S12XE-Family Reference Manual Rev. 1.19
Freescale Semiconductor
195
3.3.2.2
Mode Register (MODE)
Read: Anytime. In emulation modes read operations will return the data read from the external bus. In all
other modes the data are read from this register.
Write: Only if a transition is allowed (see
). In emulation modes write operations will be also
directed to the external bus.
The MODE bits of the MODE register are used to establish the MCU operating mode.
CAUTION
XGATE write access to this register during an CPU access which makes use
of this register could lead to unexpected results.
Address: 0x000B PRR
7
6
5
4
3
2
1
0
R
MODC
MODB
MODA
0
0
0
0
0
W
Reset
MODC
1
MODB
1
MODA
1
0
0
0
0
0
1. External signal (see
= Unimplemented or Reserved
Figure 3-4. Mode Register (MODE)
Table 3-8. MODE Field Descriptions
Field
Description
7–5
MODC,
MODB,
MODA
Mode Select Bits
— These bits control the current operating mode during RESET high (inactive). The external
mode pins MODC, MODB, and MODA determine the operating mode during RESET low (active). The state of
the pins is latched into the respective register bits after the RESET signal goes inactive (see
).
Write restrictions exist to disallow transitions between certain modes.
illustrates all allowed mode
changes. Attempting non authorized transitions will not change the MODE bits, but it will block further writes to
these register bits except in special modes.
Both transitions from normal single-chip mode to normal expanded mode and from emulation single-chip to
emulation expanded mode are only executed by writing a value of 3’b101 (write once). Writing any other value
will not change the MODE bits, but will block further writes to these register bits.
Changes of operating modes are not allowed when the device is secured, but it will block further writes to these
register bits except in special modes.
In emulation modes reading this address returns data from the external bus which has to be driven by the
emulator. It is therefore responsibility of the emulator hardware to provide the expected value (i.e. a value
corresponding to normal single chip mode while the device is in emulation single-chip mode or a value
corresponding to normal expanded mode while the device is in emulation expanded mode).
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
