Running a PIC16F628a on 3 Volt Power Supply

[Chirpy]

I have a 16f628a running at 3v also and it works fine.(2 AA batteries) As the datasheets show, they wont run above 4Mhz if run at lower voltages. If your trying to run it on a 20Mhz crystal, that may be your problem.

[SOTASOTA]

Thanks all, it appears the Brown-Out was enabled preventing operation below 4.3VDC.

Turned it off per Darrel's suggestion and "presto" all is fine!
But good points on the max frequency based on voltage. Good to keep in mind. Fortunately I am running at 4MHz. :-)