SIEMENS
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Siemens IK PI · 2015
IO-Link
Introduction
IO-Link specification
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Overview
Principles of the IO-Link specification
According to the IO-Link specification, communication functions
as follows:
•
Transmission takes place via an unshielded three-wire cable
no more than 20 m long, of the kind normally used for standard
sensors.
•
Analog values which have already been digitized are transmit-
ted in the form of message frames, which may correspond to
10 V or 4 to 20 mA.
•
Digital communication from 0 to 24 V on the so-called C/Q
cable
•
Most of the values transmitted are measured values from the
sensors which include the units.
•
The sensors and actuators are described by the
IO-Link Device Description (IODD).
•
While the IO-Link specification permits an infinite number of
ports, an IO-Link master currently only supports four ports.
Only one IO-Link device (slave) can be connected to each
port (point-to-point connection).
•
The transmission rates between IO-Link master and the
devices are as follows:
- via COM1: 4 800 Bd
- via COM2: 38 400 Bd
- via COM3: 230 400 Bd
•
The average cycle time is 2 ms for the reading/writing of 16
data bits at a transmission rate of 38 400 Bd.
IO-Link protocol
For the dialog between device and master, IO-Link uses a
standard protocol, the standard asynchronous communication
interface (UART) in "semi-duplex" mode.
The IO-Link protocol supports both the Standard IO mode (SIO)
and the IO-Link communication mode (COM).
The structure of the protocol and its message frames depends on the
types of data to be transmitted.
Data types
In the IO-Link specification a distinction is made between the fo-
llowing data types:
Process data
The process data of the devices are transmitted cyclically in a
data frame, provided the process data width does not exceed 2
bytes. In the case of larger process data widths up to 32 bytes,
parts are transmitted one after the other in several cycles. As of
Version 1.1 of the specification, up to 32 bytes of process data
can be transferred in a single cycle.
Service data (SD)
With the aid of the service data, parameter values or device
statuses can be read out. It is also possible to write the parame-
ter values or transmit commands via the service data. Service
data are always exchanged acyclically and in response to an
inquiry from the IO-Link master.
Events
Via events it is possible to transmit device events or statuses
such as contamination, overheating, short circuits etc., from the
the device via the IO-Link master to the PLC or to visualize them.
The events are sent on the initiative of the devices via the "event
flag", which the master evaluates. The master itself can also
generate events.
Three categories of event are defined:
•
Error signals (errors)
•
Maintenance data (warnings)
•
Device functions (notifications)
Data storage
As of Specification V1.1, a data storage concept has been
created for IO-Link. In this concept, the IO-Link device initiates
the storage of its data on a higher-level parameter server. In the
event that a device is replaced, the parameter server can restore
the original parameterization. It is therefore possible to replace
the devices without re-parameterization.
The IO-Link master can contain the parameter server.
The parameter server can also be implemented centrally in the
PLC or in a system server. In this case the IO-Link master passes
on the corresponding information.
IO-Link master
The IO-Link master is the interface to higher-level control sys-
tems. The IO-Link master presents itself as a normal fieldbus
node, and is integrated into the appropriate network configurator
via the relevant device description (e. g. GSD, FDCML, EDS
etc.).
IO-Link Device Description (IODD)
The IO-Link Device Description (IODD) has been defined to
provide a full, transparent description of system characteristics
as far as the IO-Link device. It is based on the open XML
standard.
The IODD contains information on communication characteris-
tics, device parameters, identification, process and diagnostics
data, and is supplied by the manufacturer. The design of the
IODD is the same for all devices from all manufacturers, and is
always presented in the same way by the IODD Interpreter Tools.
This therefore ensures that the handling is the same for all IO-
Link devices, whatever the manufacturer.
New in IO-Link Specification V1.1
The IO-Link Specification is currently available in Version 1.1,
and standardized in accordance with IEC 61131-9.
Specification V1.1 offers the following new features compared
with the previous Specification V1.0:
•
Transmission of up to 32 bytes of process or service data in
one cycle
•
Data storage concept
IO-Link master
Interface hardware:
Compatible with sensors according to IEC 60947-5-2 and actuators
Communication and switching possible alternately
IO-Link device
SIO
Standard IO
switching
operation
SIO / IO-Link
COM
Serial,
bidirectional
communication
IC01_00176
L+
C/Q
L–
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© Siemens AG 2014