CHAPTER 3: OPERATION 12-5-97 PAGE 20
3.4 DeviceNet
Control
3.4.1
DeviceNet
master (such as a scanner) can gain control of an Inverter by establishing a
Predefined Master/Slave “Polled” connection with the Option card. The master must be capable of
generating a Polled connection with fragmentation frames. During the connection, a master must also
establish an Expected Packet Rate (EPR) at which Polled messages are expected to arrive at the Option
card. Note: This timer is critical because it establishes a time delay before the Option card
assumes that communications has been lost and causes an action as defined by the Loss-of-
Network parameter.
3.4.2
Once a Poll connection has been established and the Option card is in automatic mode, Poll
data will be used to control the drive operation.
3.4.3
DeviceNet
refers to the data format passed in the Polled connection as an I/O Assembly. This
is simply multiple control parameters grouped together in a defined pattern. Two I/O Assemblies are
actually used. The first is the requesting data passed from the master to slave which contains control
data. The second is the response data returned from the slave back to the master which contains the
status. Both Assemblies are passed in a single request and response sequence. Since these formats
are set at the slave, the master must be configured to pass and receive data in the data format defined in
the Assemblies. If the Poll request issued by the master does not contain the exact number of
bytes defined by the request data assembly, a response will not be returned, and the data will not
be processed by the option card.
3.4.4
To start the drive, the master would send a Poll connection with I/O assembly values, which
would have a direction bit and a frequency value set. Thereafter, the master must either maintain these
values with re-occurring Poll messages or change them appropriately. The master can also retrieve
status information in the returned I/O assembly. Since the Option card interface to the Inverter is
somewhat slower than the network capabilities, the Option card maintains an intermediate table of values,
which are immediately available to the network. Note: Be aware that the status values returned in the
I/O assembly may be up to 750mS old.
3.4.5
When each Poll message is received, an Option card timer will be reset. The reset value of this
timer is 4 times the established EPR (Expected Packet Rate). Should that timer expire, the Option card
will take action as specified by the Loss-of-Network parameter. If the action specified is FAULT, and if
P00 status is enabled, a value indicating an EPR_TIMEOUT will be loaded.
3.5 I/O Assembly Format
3.5.1
This defines the I/O Assemblies or formats of the data passed in the Poll messages. The Input
(in terms of the master) assembly returns the status data and the Output assembly loads the Drive control
parameters. The actual size of each Assembly is dependent on the assembly length value which must be
configured in “option” function code P03 (one’s position).
Table 3-2. Assembly word length based on
Assembly length mode.
Length mode(P03)
0
1
2
Output
6
7
7
Input
2
3
4
3.5.2
Setting the assembly length mode to a value greater than zero will slightly extend the number of
data items passed in each I/O assembly. This will allow a user to pass additional configuration, status or
control items. Note: An increase in parameter numbers will add an additional fragment packet and
increase network response time.
