We have recently discovered an issue with one of our Profibus sections. We have 26 devices on this. Every so often, one or more device shows I/O Input and Output failures. Most of the time these failures clear up. However, we had an event recently when all 26 of the devices showed error and shutdown as the error didn't clear. We used the profibus tester tool with the software and found that the devices were slower than expected to respond. On the software, none of the devices responded when the timeout for the test was set at 10 seconds. As soon as we increased the timeout time to 30 seconds, all of the devices came in and had good square waves (all significantly greater than 2.5V). Every so often we still see the I/O error on this particular bus. When such an error doesn't clear immediately, we also see a device error on the profibus card. Has anyone experienced something like this?