Io-Link Basic Knowledge; Protocol; Cycle Time; Process Data Flow - Balluff BOS R254K-UUI-RS10-S4 Bedienungsanleitung

BOS R254K-UUI-RS10-S4
Photoelectric Sensors
2

IO-Link Basic Knowledge

2.1 General
IO-Link integrates conventional and intelligent sensors and
actuators in automation systems and is intended as a
communication standard below classic field buses. Field-
bus-independent transfer uses communication systems
that are already available (field buses or Ethernet-based
systems).
IO-Link devices, such as sensors and actuators, are
connected to the controlling system using a point-to-point
connection via a gateway, the IO-Link master. The IO-Link
devices are connected using commercially available
unshielded standard sensor cables.
Communication is based on a standard UART protocol
with a 24-V pulse modulation in half-duplex operation. This
allows classic three-conductor physics.
2.2

Protocol

With IO-Link communication, permanently defined frames
are cyclically exchanged between the IO-Link master and
the IO-Link device. In this protocol, both process and on
demand data, such as parameters or diagnostic data, is
transferred. The size and the type of the frame and the
cycle time used result from the combination of master and
device features (see communication properties in section
3.2 on page 9).
2.3

Cycle Time

The cycle time used (master cycle time) results from the
minimum possible cycle time of the IO-Link device
(min cycle time, see section 3.2 on page 9) and the
minimum possible cycle time of the IO-Link master. When
selecting the IO-Link master, please note that the larger
value determines the cycle time used.
2.4

Process Data Flow

The data transfer is based on the general profile
specification (IO-Link Common Profile 1.0, see Fig. 2-1 for
example).
PDinput data stream (device view)
Transmission
direction n n+1
("to master")
39 30 31 24
...
Byte 0 Byte 1
7 0 7 0
Integer16
"PDV2" "PDV1"
PVinD 3 PVinD 2
Data type: IntegerT Data type: UIntegerT
TypeLength: 16 TypeLength: 8
Bit offset: 24 Bit offset: 8
Example PDinput data stream
Fig. 2-1: Example of a PDinput data flow
6 english
n+3 n+4 memory address in the PLC
n = baseaddress
15 8 7 0 Bit offset
Byte 3 Byte 4
7 0 7 0 Byte stream
UInteger8 Bool
"BDC1_2"
PVinD 1
Data type: Bool
TypeLength: 2
Bit offset: 0
The highest value byte (MSB, designated as Byte 0 ) is
transferred first and can be found in the PLC under the
lowest storage address. The lowest value byte (LSB) is
transferred last and has the highest byte number
(designated in Fig. 2-1 as Byte 4).
For word-based data types (> 8 bit) this means that the
byte at the lowest address is the highest value byte, while
the highest address contains the lowest value byte.
In the IODD, the description of the data flow is realized
using the skew descriptors. This skew starts at the right
with the lowest value byte.
Process data variables (in Fig. 2-1: PDV1, PDV2) are
aligned to the byte limits in most cases.
Binary information (BDC) is transferred in the lowest value
byte in most cases.
2.5

Device Status

The Device Status indicates the current status of the
device or of the directly connected peripherals. This
functionality is part of the IO-Link specification.
The following states are output by the device:
– Device is operating properly (device is functioning
error-free)
This status indicates that no serious error has occurred
in the device and the device can be operated without
restrictions.
– Maintenance-Required
Although the process data is valid, internal diagnosis
functions show that the device or the operational
environment of the device should be serviced.
– Out-of-Specification
Although the process data is valid, internal diagnosis
functions show that the device is operating outside of
the specified specification. This can affect both the
measurement application itself as well as the
environmental conditions.
– Functional-Check
Process data is temporarily invalid while a deliberate
intervention is performed on the device. For example,
parameterization processes or teach-in.
– Failure
The device or the connected peripherals have a severe
error. The device cannot perform its intended function!
For further information, see section 6.1 on page 66.
The creation of the Device Status is always based on the
output of diagnosis messages. A Device Status is output
for every diagnosis message (event). Each of these can be
found in the event overview list (see section 3.6 on
page 22) or in the description of the functions.