Modbus/TCP driver compatibility issue

[fsturlese]

Hello all,

we have found a problem that can be reproduced this way:
- create a project with iX 1.31, using the Modbus/TCP default driver (5.07.01). The default node number will be set to 0, even if new stations are added. Everything will be working fine.
- install iX 2.0 for evaluation, while keep using iX 1.31 for your ongoing projects
- after the installation of iX 2.0, open the old project with iX 1.31: it won't work any longer.

After a few hours spent trying to understand this weird behavior, we found that iX 2.0 installs a newer version of the Modbus/TCP driver (5.10.xx) which implements a new feature, i.e., the broadcast addressing (with node=0). The drivers are stored in the same folder for both 1.31 and 2.0, so after having installed 2.0, the new driver will be active for 1.31 as well, and will prevent the older 1.31 projects, created with node=0, from working correctly.

Note that the help of the 5.10.xx driver states that setting node=0 will return no data, but there is obviously no trace of this in the help of the driver 5.07.01, so there was no way to know this by the time the project was created.

This is a serious backward compatibility problem, and a there are a number of questionable issues related:
- when automatically upgrading a project to a new version of the driver, at least a warning message should be issued (this happened in Information Designer)
- when introducing a new feature (broadcast address, in this case), A LOT of care should be taken to backward compatibility. Features that modify the behavior of existing projects bring a waste of time and money to fix them in field. A clever way to introduce this feature would have been to assign 255 to broadcast, instead of 0 that was a value obviously already used in old projects.
- once introduced the feature, the default value proposed by iX when adding a new station should be 1, instead of 0 that is not working.

I hope this helps avoiding similar problems in the future.
Regards,
Federico.

[Ron L.]

Discussed on:
http://ixtalk.beijerelectronics.us/view ... f=5&t=1278