@Neo:
I saw that you mentioned using just one crystal to feed several clocklines, does this work without any problem?
@danamania:
If I recall correctly, the low voltage 68040 version supports from 0 to MAX MHz officially. Dont know about the standard 68040, though 8MHz should be ok. This would be useful when constructing something experimental on a lab-board or something similar as such an environment introduce a lot of crosstalk, signal disturbance, etc making it hard to run at high clock speeds.
/Patrik
