Contrologix API

Can someone give me a detailed explanation of the API in contrologix and how it factors into the RPI settings?

I think I know what you mean by RPI - "Requested Packet Interval", but don't know what you mean by "API".

In my knowledge API is an acronym for .... "An application programming interface (API) is a particular set of rules and specifications that a software program can follow to access and make use of the services and resources provided by another particular software program that implements that API. It serves as an interface between different software programs and facilitates their interaction, similar to the way the user interface facilitates interaction between humans and computers."

API in this respect stands for Actual Packet Interval.

Basically it refers to the actual time that requested data will be delivered. In ControlNet because of it's scheduled data transmissions this can be calculated, but I am not sure that API figures can be calculated for EtherNet/IP for anything but best or worst case.

For ControlNet the API will be binary multiples of the Network Update Time (NUT). So given a 5ms NUT then the API values would be: 5, 10, 20, 40, 80ms. The API will be the closest lowest interval. So in the example I used if you ask for a 19ms RPI you would get 10ms. If you asked for 21ms you would get 20ms.

OG

OG

sorry i was not more specific but yes i was primarily asking in reference to ethernet ip but thaanks for the controlnet info also. I was reading some KB notes on RPI and API but i could not find any that gave a good description of the working correlation between the two.


So from your post i gather that on E/IP it is a calculation that may vary a bit but on controlnet it is pretty well within the calculated time correct?

OG

Is there a way the API can be logged so the API can be directly compared to the RPI. Where would you access this data and could it be also have a time stamp.

Could the API be identified using wireshark?

Sure you can use Wireshark. You can also setup the I/O modules for CST Timestamping. That is assuming you are referring to I/O data. You can compare changes in data to the CST.

OG

In every case I can think of the, Requested Packet Interval and Actual Packet Interval will be the same on EtherNet/IP.

You can capture the ControlLogix and the I/O adapter negotiating the Connection, and the RPI and API are explicitly communicated in that exchange.

The built-in Web interface for the 1756-ENBT and -EN2T shows the API for each I/O connection and Produced/Consumed Tag.

And you can implicitly measure the API using Wireshark by filtering out a specific CIP connection number, and measuring the time between displayed packets. I've done this to prove performance for a skeptical user.

Thanks guy's