I/O driver

An I/O driver in the world of CODESYS is a piece of software, that abstracts the access to a piece of hardware, which usually provides input data (like temperatures, switches, ...) or drives outputs (analog, digital, PWM, ...).

The way to use those I/Os is usually, to add the modules to the device tree of your CODESYS project, configure them and map the input and output channels to variables i your application.

Function Block

When start writing an I/O driver in IEC, the best way is to start with a function block. The reason is, that it is very easy to pass the input and output values of your hardware to the inputs and outputs of your FB.

Try to keep the interface of the FB as simple as possible, and do all the work, which is necessary to handle the hardware in the main POU of the FB.

So if you for example read a value of a sensor through SPI, name the input of the FB accordingly, and code the SPI access inside of your FB.

I/O driver interface

When you have such an FB, it becomes very straight forward to write an I/O driver frame around that, so that the user can easily add this driver to his project, like he is used to do it with other fieldbusses in CODESYS.

Device Description

Mapping the I/Os

Reading / Writing I/Os