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Chapter 18 External Bus Interface (S12XEBIV4)
MC9S12XF - Family Reference Manual, Rev.1.19
Freescale Semiconductor
829
internal RAM and misaligned XGATE PRR accesses in emulation modes are the only type of access that
are able to produce LSTRB = ADDR0 = 1. This is summarized in
Table 18-19.
18.4.6
Low-Power Options
The XEBI does not support any user-controlled options for reducing power consumption.
18.4.6.1
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.
18.4.6.2
Wait Mode
The XEBI does not support any options for reducing power in wait mode.
18.4.6.3
Stop Mode
The XEBI will cease to function in stop mode.
18.5
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
Table 18-19. Access in Emulation Modes and Special Test Mode
Access
RW
LSTRB ADDR0
DATA[15:8]
DATA[7:0]
I/O
data(addr)
I/O
data(addr)
Word write of data on DATA[15:0] at an even and even+1
address
0
Out
data(even)
Out
data(odd)
Byte write of data on DATA[7:0] at an odd address
0
1
In
x
Out
data(odd)
Byte write of data on DATA[15:8] at an even address
0
1
0
Out
data(odd)
In
x
Word write at an odd and odd+1 internal RAM address
(misaligned — only in emulation modes)
0
1
Out data(odd+1) Out
data(odd)
Word read of data on DATA[15:0] at an even and even+1
address
1
0
In
data(even)
In
data(even+1)
Byte read of data on DATA[7:0] at an odd address
1
0
1
In
x
In
data(odd)
Byte read of data on DATA[15:8] at an even address
1
0
In
data(even)
In
x
Word read at an odd and odd+1 internal RAM address
(misaligned - only in emulation modes)
1
In
data(odd+1)
In
data(odd)