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Chapter 5 External Bus Interface (S12XEBIV4)
MC9S12XE-Family Reference Manual Rev. 1.07
Freescale Semiconductor
249
5.4.2
Internal Visibility
Internal visibility allows the observation of the internal CPU address and data bus as well as the
determination of the access source and the CPU pipe (queue) status through the external bus interface.
Internalvisibilityisalwaysenabledinemulationsinglechipmodeandemulationexpandedmode.Internal
CPU accesses are made visible on the external bus interface except CPU execution of BDM firmware
instructions.
Internal reads are made visible on ADDRx/IVDx (address and read data multiplexed, see
Table 5-11
to
Table 5-13
), internal writes on ADDRx and DATAx (see
Table 5-14
to
Table 5-16
). RW and LSTRB
show the type of access. External read data are also visible on IVDx.
During ‘no access’ cycles RW is held in read position while LSTRB is undetermined.
All accesses which make use of the external bus interface are considered external accesses.
5.4.2.1
Access Source Signals (ACC)
The access source can be determined from the external bus control signals ACC[2:0] as shown in
Table 5-9
.
Table 5-9. Determining Access Source from Control Signals
Data select signals
(if 16-bit data bus)
—
—
UDS
LDS
ADDR0
LSTRB
ADDR0
LSTRB
ADDR0
LSTRB
Data direction signals
—
—
RE
WE
RW
RW
RW
Chip Selects
—
—
CS0
CS1
CS2
CS3
—
CS0
CS1
CS2
CS3
—
External wait
feature
—
—
EWAIT
—
EWAIT
—
Reduced input
threshold enabled on
—
—
Refer to
Table 5-3
DATA[15:0]
EWAIT
DATA[15:0]
EWAIT
Refer to
Table 5-3
1
Incl. S12X_EBI registers
2
Refer to S12X_MMC section.
3
If EWAIT enabled for at least one CSx line (refer to S12X_MMC section), the minimum number of external bus cycles is 3.
4
Available only if configured appropriately by ROMON and EROMON (refer to S12X_MMC section).
ACC[2:0]
Access Description
000
Repetition of previous access cycle
001
CPU access
010
BDM external access
Table 5-8. Summary of Functions
Properties
(if Enabled)
Single-Chip Modes
Expanded Modes
Normal
Single-Chip
Special
Single-Chip
Normal
Expanded
Emulation
Single-Chip
Emulation
Expanded
Special
Test