CompactLogix v20 Bad_CommunicationError

[pturmel]

You must use the v21+ driver for firmware v20.19, due to Rockwell cutting off the high-performance but totally insecure memory access services that the legacy driver relies on. See this topic:

CIP Connection Size Parameter

There’s 2 drivers: the “legacy” driver that works with firmware v20.13ish and prior, and the new “Logix Driver” that works with any firmware version but is optimized for v21+. The new driver is not faster than the old driver. The old driver reads tag values directly out of memory. Rockwell disabled this functionality starting in 20.15? or something like that. In 21+ they introduced a new API for reading tags based on instance IDs (instead of via symbolic names). The new API is certainly faster…