GE Industrial Solutions OKCV3000CN DeviceNet - Manual (Page 31)

DeviceNet
5. LOCALBUS: HOW TO EXCHANGE I/O DATA
5.1. MASTER/SLAVE CONVERSATIONS
A “conversation” is the execution of multiple transmissions and receptions between a Master and a Slave over
the DeviceNet serial network. All conversations are executed by dedicated communication Bricks in the Master.
This kind of Brick specifies which Slave to communicate with and to execute conversations with. It also speci-
fies which Master IVARs are to be sent to the Slave (and where to put the received words from the slave) and
which Slave words of FWA are to be received from the Slave (and where to put the received values from the
master).
The Master always initiates a conversation with a Slave. The last frame of any conversation must always be a
frame response from the Slave. The first word of each frame sent from Master to Slave or from Slave to Master
will always be aCODE word which describes the construction ofthe conversation (which FWA values are to be
sent to the slave device, in form of data words, and which FWA values are to be fetched from the slave device,
in form of data words).
A conversation may specify that 0, 1, 2 or 3 words of FWA have to be received from a Slave and 0, 1, 2 or 3
IVARs are to be sent to the Slave. The Master device sends its IVAR and receives in its IVAR. The values
associated with Fixed Word (s) can be exchanged at every Bricks execution time of the Master device.
The CODE word specifies the number of Fixed Words to be received from the slave.
5.2. CONNECTING TOGETHER DEVICENET CARDS
The DGFC is able to communicate easily with other DGFC Clients or Servers by programming every communi-
cation via Bricks. For each DGFC card the limits on the other DGFC that may be connected with DeviceNet line
are:
-
the DGFC can have 3 different DGFC masters
-
the DGFC can have 63 other DGFC slaves. The first slaves use an individual communication channel and
are called ICS Server “Individual Channel Server”. All other slaves use the same communication chan-
nel, so they are called SCS Server “Shared Channel Server”.
Note that DeviceNet supports up to 64 devices.
The ICS server allows powering off the device without influencing the other communications; also errors on
other channels do not affect these communications.
The SCS servers communicate using the same channel of the CAN Controller chip. This means that if one slave
goes off, the first communication with this slave has no answer and the device is disconnected only after the
time-out elapse. During this time, the communication with the other SCS servers is not possible. Only after the
disconnection of this device, can the communication with the other Servers continue.
The ICS servers are the first seven servers on Bricks program with different MACID starting from CFIX 0 block.
HOW TO EXCHANGE 110 DATA