TwinCAT ADS Interface PLC

The PLC software can be described as a virtual field unit (Automation Device), since it is a pure software PLC. It therefore provides a Beckhoff ADS (Automation Device Specification) interface for other communication partners (e.g. other virtual field units or Windows programs), via which it can be parameterised or interrogated. Use of the ADS standardises access to the PLC and incorporates it into the range of available virtual field units.

The READ and WRITE operations take place on the PLC interface (as defined by ADS) via two numbers: the index group (16 bit) and the index offset (32 bit). The ADS interface of the PLC will be described in more detail in the following pages with regard to the group and offset indices.

Specification "Index-Group" of the PLC

The four global ranges of an ADS unit are shown as follows for the PLC as four sections in the index groups:

Index-Group

(0x = hex)

Index Group description

0x00000000

0x00000FFF

reserved

0x00001000

PLC ADS parameter range

0x00002000

PLC ADS status range

0x00003000

PLC ADS unit function range

0x00004000

PLC ADS services ( includes services to access PLC memory range (%M field) )

0x00006000

0x0000EFFF

reserved for PLC ADS extension

0x0000F000

0x0000FFFF

general TwinCAT ADS system services ( includes services to acces PLC process diagramm of the physical inputs and outputs )