Some people have had trouble loading their interrupt vector code into
the simulator.  (A dialog box pops up that says "Unable to write
address" or something similar.)  This seems to occur when people
select 'MPC821' as the processor type.  Note that this problem applies
to the simulator only; debugging on the target boards using the
on-chip debugger should work the same way it always has.

There are two ways to fix this:

1) In the Debug dialog box, under the Processor tab, select '601' for
the processor type.  Even though this isn't what we're using in the
lab, for the code you can run on the simulator it shouldn't matter.

OR

2) In the Debug dialog box, under the Processor tab, continue to
select 'MPC821' for the processor type.  When the Debug dialog first
appears, cancel it, and in the command window type the following two
commands:

alias _load '_config ; load $debugblk:q'
alias _reset '_config'

Then bring up the debug window again (type ctrl+d or use the file
menu) and it should work.  You should only have to type these commands
when you first start SingleStep; if you reload your program via the
Debug menu it should continue to work.