High freq, low voltage - what happens if?

[kevj]

I've been working up a design that needs 20Mhz at a 3.3v supply. I'm using a 16F677 and everything is working fine, but I just realized the data sheet notes in electrical specifications that there is a max speed for given voltages.

The graph is a grey shaded block area that shows 20mhz is only allowed at > 4.5v supply, and that 10Mhz is the max allowed at a supply of 3.0, 3.3v. The note just says "The shaded region indicates the permissible combinations of voltage and frequency."


So what happens if I'm running outside this range? Could the program occasionally hang? Not sure what to make of this.

Thanks.

[Charles Linquis]

Running in the "gray" area means that the chip is not GUARANTEED to work, even though any particular one may. Another chip (even if it of the same type) may not work at all. The chip may also stop working at temperature extremes.

I don't know if one is available that meets your needs, but why don't you use one of the 18FxxJxx series chips? They are guaranteed to run full-speed at 3.3V.

[tenaja]

This is similar to overclocking your PC. It might work... for now.

Kind of like what Charles said.