00 or 01?

[Marteney, Steven J.]

I don't think I would ever use $00 unless you are POSITIVE the code is data
only!  $00 is an opcode for TEST which is only valid in test mode only
(according to the Motorola HC11A8 Ref manual).  $01 is the opcode for a NOP.
The processor will happily bounce on over it and do nothing, just waste an
execution cycle.  If you happen to know the portion of code you are
overwriting is a branch type instruction use opcode $21, which is the branch
never instruction.  Of course, when deleting code with $01, make SURE you
replace all the data items to follow with $01 as well.  If you don't, you'll
hit an unwanted valid or invalid opcode and send the processor into lala
land and hopefully generate a watchdog reset or illegal opcode interrupt.
Don't what will happen driving down the road and have that happen.

HTH, Steve

-----Original Message-----
From: Bruce [mailto:nacelp at bright.net]
Sent: Friday, August 13, 1999 8:23 AM
To: gmecm at diy-efi.org
Subject: 00 or 01?


When do you want to use one vs the other (00 vs 01) when eliminating some
code?.
Or is it a matter of you have to just try it?.
TIA
Bruce
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