Background to the question - I used several bits in a particular RAM byte as flags. They would be set at power up if certain external conditions were yes. The mistake I made was not clearing the RAM first, and so sometimes those bits that should have been clear would be randomly set...
So, the question is, if a bit is not specifically set or cleared at power up, can it be kind of borderline halfway and perhaps be read as a 0 for a while and later drift be read as a 1? Sort of like when an input pin is left floating and eventually drifts across the low/hi threshold.
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I never picked up this non-cleared RAM problem until just now. HC908 micros never gave a problem for quite a few years. Switched to S08PA micros three years ago and still no problems. Then switched to S08FL because of chip shortages and this is where it all started. Those micros have been a pain in the butt for a number of reasons, but it's an ill wind that blows nobody no good. At least I found a bug that I probably wouldn't have otherwise.