|I am using an HC12 device in expanded mode, are there some special considerations for this?
|Application Note : 68HC12 Expanded Mode Operation
Up in Single Chip Mode
Starting up in special single chip mode is very simple. When the MODA
and MODB are
both grounded, and PEmicro’s BDM cable is used to reset the processor,
the processor will
start in single chip mode. The processor, after reset, immediately goes
into a halted state
waiting for instructions from the BDM port to either program or debug
Up in Expanded Narrow and Expanded Wide Modes
Starting up in either expanded mode is not as clean cut as starting in
Expanded operation is enabled when the MODA pin is high when PEmicro’s
resets the processor.
The difficulty in using these modes usually occurs immediately after
reset. Unlike the
single chip mode, the processor doesn’t enter a halted state, but
instead starts executing
instructions. This can be troublesome because before PEmicro can
command the processor to
halt, the processor registers may have been altered by fixed or random
code which is
executing. Even if the user has something programmed into flash, this
program will be
running for a specified amount of time after reset. This is a drawback
to the expanded
background mode operation, so what to do about it?
(1) This is the recommended
solution. If you do not wish code to run a startup, or you are
unable to reset the target, change your jumpers to boot the part into
chip mode. The reason special single chips starts in a halted state is
to allow expanded
targets with blank flash to ALWAYS be boot-able. At this point you have
the MODE register to select the expanded mode you want. Note, however,
registers may not be set up properly for the expanded mode, and you may
have to set
them up yourself with a script file (such as chip select registers).
This is the only
guaranteed way to be able to boot an expanded mode target.
PEmicro’s In-circuit Debugger comes with script files for the 68HC812A4
run, will switch the part from Single Chip mode to either Narrow
(A4NARROW.ICD) mode or Wide Expanded (A4WIDE.ICD) mode. These script
files come from booting the chip properly in each of the three modes,
differences in the register values. You must run the script file
whenever you reset the
processor. PEmicro’s cable, debugger, and flash programmer work for any
device, and to use this method for other HC12 devices in the expanded
would write a similar script file to change the mode.
PEmicro’s Flash Programmer comes with programming algorithm files which
automatically place the chip into the proper mode. Hence, the chip can
single chip mode, via MODA and MODB settings, and the programmer will
automatically change the mode. This method can be seen by looking at the
initialization section of one of PEmicro’s external programming
(2) This works, but is not the
recommended solution. You can RESET the target via the
software (NOT a target reset switch) until the target starts up.
Sometimes it takes two,
three, or more resets (RETRYs) before the target starts properly. Note
that when the
processor starts up properly, you can use it normally, as long as you
all the registers might not be configured as they are out of reset.
Most of the time this
will not be an issue, but this startup mode is not deterministic in
terms of register
configuration as is booting into special single chip mode.
You can see this using the Motorola HC12A4EVB. If you set this up for
wide mode operation with the RAM in the memory map, you will see that
it takes two
or three resets before the processor starts up properly and allows the
debugger to take
control. At this point write a word at address $FFFF equal to the value
then put a loop at address $E000 such as
You will see at this point the processor will start up perfectly every
attempting a reset. This is because the processor, upon reset, jumps to
this loop and
runs harmlessly until PEmicro issues the background HALT command a
short while later.
|| Interface Hardware/Cable, Debugger, Flash Programming Software, Stand-Alone Programmer
|| CYCLONEPRO, ICD12Z, PKG12Z_USB, PROG12Z, DEMOJM, XPC560PKIT100S, XPC560SADPT280S, XPC560SADPT144S
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