There have been numerous applications in the ESP8266, I have taken as a goal to integrate this module into one of the industrial protocols most commonly used Modbus TCP IP, it would be good to have a node or sensor that sends data or a driver, OPC, PAC, PLC, HMI or SCADA.
More information on this project :
Step 1: Background
A long time ago I found a group of people in forums.adafruit already had an advance and example have been implemented and improvements suggested by ibbba for the contribution.
The programming code for ESP8266 in this case was implemented in Arduino IDE versions 1.6.4 above. These 2 tutorials indicate connection and basic programming ESP8266 01 and 03 modules.
With the new modifications it has been omitted disconnection allowing a constant flow of communication if stop the connection between the ESP8266 and modbus tcp master mandatory.
He has implemented Ticker library created and documented by igrr, it is an object to call a given function with a certain period. Each Ticker calls a function. You can have as many as you like tickers, the only memory limitation.
Important note: When creating tickers consider not create any delay would affect both modbus communication protocol, such as the execution of that function.