AN2104 Freescale Semiconductor, AN2104 Datasheet - Page 9

• Manufacturer Part Number: AN2104
• Description: Using Background Debug Mode
• Manufacturer: Freescale Semiconductor

AN2104
These examples deal with the levels on the BKGD, MODA, and MODB
pins during a reset to determine which mode the part will come up in. The
user can also change the mode of operation by writing to the mode
register after the part is powered up. See
The MODE register can be read at any time. However, writing to this
register presents some restrictions. First, if the part comes up in the
normal mode, it can be changed only to another normal mode. This
change can be done only once.
The special mode does not have this limitation, since the values of the
MODA and MODB pins can be changed as many times as desired as
long as the part remains in special mode.
Next, coming up in the special mode, the part can change to the normal
mode, but must write to the SMODN bit in this register two times, as the
first write is ignored.
BKGD MODB MODA
Freescale Semiconductor, Inc.
0
0
0
0
1
1
1
1
For More Information On This Product,
0
0
1
1
0
0
1
1
Go to: www.freescale.com
0
1
0
1
0
1
0
1
Table 4. Mode Selection
Special expanded narrow
Normal expanded narrow
Special expanded wide
Normal expanded wide
(forced to peripheral)
Special single chip
Normal single chip
Special peripheral
Reserved
Mode
Figure
M68HC12 Operating Modes
ADDR[15:8]
ADDR[15:8]
purpose I/O
purpose I/O
5.
DATA[7:0]
DATA[7:0]
General-
General-
Port A
ADDR
ADDR
ADDR
DATA
DATA
DATA
—
Application Note
purpose I/O
purpose I/O
ADDR[7:0]
ADDR[7:0]
General-
General-
Port B
ADDR
ADDR
ADDR
DATA
DATA
DATA
—
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