Are you certian that you're running your device within parameters?

3-5VDC, 0C to 70C, 10MHz at 3v, 20MHz at 4.5v
Above and below that temperature range you need 4.5v to run above 4MHz.

You ought to get in touch with your Microchip representative.  It could
well be that there's a known issue with a particular run or batch -
sometimes only the reps have knowledge of this type of information.

-Adam

Nigel Orr wrote:

>We have recently had a couple of devices (16F628) with faulty RAM addresses.
>Fortunately they were caught during quality control, but I'm a bit concerned
>that it could have a more subtle effect, if the fault had occurred in a
>different byte.
>
>Two bytes (0x74 and 0x78) had a 'sticky' 1 in bit 6.  If I write 0xFF, I
>read 0xFF, if I write 0x00, I read 0x40.
>
>Has anyone come across this before?  It happens constantly on 1 device, and
>happened intermittently on 3 others.  I've tested over 20 from the same
>batch which have shown no faults.
>
>I could add RAM checking code to the device, but code space is short, as
>usual, and there would still be faults which are not detected.
>
>Nigel
>
>
>
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