Baumer GK473 - Manual (Page 9)

Manual_GK473_DeviceNet_EN.doc 9/31 Baumer IVO GmbH & Co. KG
04.05.11 Villingen-Schwenningen, Germany
5 DeviceNet interface description
5.1 Data exchange DeviceNet Master <-> Slave
DeviceNet was developed by Rockwell Automation and the ODVA (Open DeviceNet Vendor Association) as
an open fieldbus communication standard based on CAN protocol. DeviceNet is in line with European
Standard EN 50325 and specified and administered by ODVA. DeviceNet is an object-oriented bus system
operating according to the producer/consumer communication principle. DeviceNet appliances can be client
(Master) or server (Slave) or even both. Client and server may be either producer, consumer or both.
Layer 2 (Data Link Layer) is based on the Controller Area Network (CAN).
The DeviceNet network is a connecting structure for communication between maximum 64 bus users utilizing
Baudrates of 125, 250 or 500 kBaud. The DeviceNet topology provides besides the two signals CAN-L and
CAN-H for data transmission also two 24 VDC supply lines enabling the DeviceNet users to be directly
powered from the bus or from an external source (GK473 external supply only). The maximum length of the
DeviceNet depends on the selected cable size and Baudrate. Installation is according to bus topology –
trunkline/dropline- with bilateral terminating resistors. The terminating resistors provide 120 Ohm.
GK473 DeviceNet gateway operates as a Class 2 Slave in the DeviceNet bus network. The device supports
I/O Poll connections and Change-Of-State messages of the predefined Master Slave Connection Set. It does
not support "Explicit Unconnected Message Manager" (UCMM).
I/O Poll
While polling the DeviceNet-Master is transmitting a Poll Request to GK473 replied by the status information
stored in the GK473 on the connected RS485 sub bus and users .
The 48 Byte data packet comprises the following information:
The individual bits represent the respective status at the relating sub bus ID.
Byte 0..15 “SPA not in position”
Byte 16..31 “SPA in error state”
Byte 32..47 “SPA in time out state”
COS (Change of State)
The data content is according to I/O Poll.
GK473 will only produce and transfer data to the DeviceNet master upon any change of state at the RS485
sub bus. Utilizing the Change-of-State messages means a considerable reduction of data volume in the
DeviceNet bus.
After having implemented the COS connection user data amounting to 48 bytes will be transmitted once.
Second the message will only be transmitted (produced) if the previous state changes.
Advantage:
Normally all bytes are 0 -> all SPA’s are in position, no SPA error and no SPA time out.
Input data for the control will be only produced upon change of state.
This way the bus load is kept down to a minimum.