??? 07/12/05 01:01 Read: times |
#97109 - Noise problems? Responding to: ???'s previous message |
Bartosz Wucke said:
Found myself in this situation several times. Usually at the second appearance of the bug I was doing everything "not to fix it accidentially", but usually I would fail. And once the problem mysteriously goes away, finding it (and fixing it the RIGHT way) becomes near-impossible. Any suggestions against it? Noise problems tend not to show up until the system is installed and operating in its intended environment. Then, after a few minutes or hours of normal operation the system finds itself someplace out in left field. Inputs are ignored and outputs are gibberish. The system may respond to a reset, or it may have to be turned off physically and then back on again, at which point it commences operating as though nothing had happened. There may be an obvious cause, such as an electrostatic discharge from somebody's finger to a keyboard or the upset occurs every time a copier machine is turned on or off. Or there may be no obvious cause, and nothing the operator can do will make the upset repeat itself. But a few minutes, or a few hours, or a few days later it happens again.One symptom of electrical noise problems is randomness, both in the occurrence of the problem and in what the system does in its failure. All operational upsets that occur at seemingly random intervals are not necessarily caused by noise in the system. Marginal VCC, inadequate decoupling, rarely encountered software conditions, or timing coincidences can produce upsets that seem to occur randomly. On the other hand, some noise sources can produce upsets downright periodically. Nevertheless, the more difficult it is to characterize anupset as to cause and effect, the more likely it is to be a noise problem. Designing Microcontroller Systems for Noisy Environments |