The Industrial Raspberry Pi Forum

Hi All
As I understand the DI/DO modules is using the RS485 bus to communicate the RPi board.
How fast reaction time can I expect from an input is changed to the software is notified.
I have plans to write the program in C++, and how do I subscribe to the DI changes so I don't have to poll?

Hi hholst, the reaction time depends on the amount of modules and the configuration. you may read the value out by . This value is the amount of ms without rounding up or down. So 2 may also mean 2.9 ms which leads to about 6 ms worst case. Currently there is no other option than polling.

For the local GPIO pin's at the RPI board it is possible to get a notification using the IOctrl I can see in the WiringPI project.
So it is really a shame you have not from the beginning designed the inputs to be able to give an interrupt signal.
I can see the MAX31913 you use in the DI module does not either support an interrupt pin, but you could have implemented in the STM32F205 software a polling routine which could notify the RPI module via a RPI GPIO pin
I am looking for a maximum guarantied reaction time of 1ms

Dear hholst, well thank you for your words. If you have a requirement of 1ms reaction time then the RevPi is unfortunately not fast enough today.