ICC DNET-100, User Manual

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12.2 I/O Assemblies
Now that we have been exposed to the concepts of parameter mapping and
access, let’s further expand upon this concept to include the configuration of
I/O assemblies. The DNET-100 supports four I/O assembly objects, whose
instance numbers are defined as follows:
Polled I/O output assembly............................ instance #100 (0x64)
Polled I/O input assembly.............................. instance #150 (0x96)
COS/cyclic I/O output assembly .................... instance #101 (0x65)
COS/cyclic I/O input assembly ...................... instance #151 (0x97)
The sizes and member lists of these assembly objects are entirely user-
configurable, and the configuration of each assembly object is independent of
the others. The assembly sizes (consumed data for output assemblies and
produced data for input assemblies) are selectable from 0 to 200 bytes, in 2-
byte increments. The reason for the 2-byte increment restriction is due to the
fact that all secondary-network data object values for protocols supported by
the DNET-100 are 16 bits in size. Any valid DeviceNet parameter currently
defined in the gateway can be included in the member list of any of the I/O
assemblies.
To see how this works, we will continue our example network that we started in
the previous section. Now, however, we are interested in adding DeviceNet
scanner access to the 12 parameters that we previously defined. First, we
need to determine which parameters are command-oriented (parameters that
we will write to with the intent on performing some action) and which are
status-oriented (parameters that we will monitor with the intent of determining a
data object’s status). From Table 4, we can see that parameters 1, 3 and 6
are command-oriented, and the rest are status-oriented.
Our next decision is to determine which I/O assemblies we will use (poll, COS,
cyclic, poll+COS or poll+cyclic). This decision is typically based on the specific
nature of each application, and must be determined by the person performing
the network configuration. For this example, we will use Polled I/O only, and
will therefore only need to configure the characteristics of assembly instances
100 and 150.
To determine the required sizes of the I/O assembly instances, we can
recognize the fact that the “value” attributes of all DNET-100 parameters are
16 bits (2 bytes) in length. This results in the following formula:
Number of parameters in member list x 2 = size of assembly in bytes
For assembly instance 100 (our command assembly), therefore, we can use
the above equation with our previous determination of having 3 command-
oriented parameters to arrive at a consumed data size of 6 bytes. Similarly,
the produced data size for assembly instance 150 can be calculated to be 18
bytes. These size definitions are then entered into the DNET-100’s console.
Note that in this example we have chosen to include all available parameters