Introduction

By using the I/O Extension functionality, it becomes extremely simple to extend the number and the diversity of I/Os beyond those that are available natively on the RTCU device by adding cost-effective external I/O modules.

The I/O Extension functionality offers the following key features:

•High performance fail-safe MODBUS implementation - RTU protocol version.

•Uses industry standard MODBUS-based I/O modules

•Physical layer used is RS-485 available as a standard or option feature.

•MODBUS master mode supports seamless I/O extension with up to 64 I/O modules and 1024 * I/O points.

•MODBUS slave mode support operating as an I/O node under the control of for example a SCADA system.

•MODBUS master and slave mode can operate simultaneously in advanced application scenarios.

•Fully transparent I/O extension. This means that resources on external I/O modules become an integral part of the on-board I/O subsystem.

•Automatic run-time I/O maintenance. This means that absolutely no application handling is required to operate the I/O extension.

•Comprehensive exception handling paradigm for support of mission critical applications.

•Almost any standard MODBUS I/O module can be used but modules offered by Logic IO are especially easy to set up and have hassle-free operation.

Using the I/O Extension functionality is extremely simple, and it is recommended to go through the Using the I/O Extension (master mode) section of this manual to get the best and fastest working experience. Within a few minutes, it is possible to configure and use MODBUS-based remote I/O as if they were an integral part of the on-board I/Os.

The I/O Extension functionality requires no VPL application support to work as everything is operated automatically by the powerful firmware-based I/O manager. Please note that for the same reason IOs which are controlled by another MODBUS master in slave mode must not be mapped in the Job as updates done by the firmware-based I/O manager will be overwritten by the application I/O manager. Please see Using the I/O Extension (slave mode) for implementation reference.

For specialised applications where full control of the MODBUS communication is required, it is possible to bypass the I/O Extension and use basic MODBUS communication primitives that allow transmission and reception of data according to the MODBUS protocol. Please reference the MODBUS API section for further information.

The in- and outputs on external I/O devices are updated asynchronously with the on-board I/O to ensure that the communication required will not slow down the execution of the application.

There is also an option for synchronous updates if such is required (see ioSetMode for the possible update modes).