Hello Lyman,
The CW5.1 not support Windows 10 :

So now you only can test the CW v5.2 , it support Win10, while it not directly includes the chip of
"MC9S12DG256 " , there is a method to add missing products on CW v5.2, you can have a try.
Add missing derivatives to CodeWarrior HCS12(X) 5.2 (Unofficial Method)
Have a great day,
Alice Yang
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