Hello,

A node that supports a direct communication to the ICSP interface of the IOT currently does not exist. These are the possibilities you have:

1. Create and own node-red node, that communicates SPI over the mraa library. As you see, the SPI is part of libmraa, so these functions should also be available in javascript
2. Use Arduino sketch to get your data from SPI, then send it over MQTT mosquitto broker
3. Use Arduino sketch to get your data from SPI and send it over the linux filesystem. In node-red there is also the possibility to read a file and extract the data again.
4. Use the mraa library in C++ and instead of using node-red you can utilize the snap7 library to establish an S7 connection to the S7-300

Many ways lead to Rome. In my opinion Nr. 1 and 4 are the more elegant solutions.

Kind regards!