ICC DNET-100, User Manual

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as members of I/O assemblies. There is no requirement to do this, however: it
is perfectly acceptable to define a stand-alone parameter which is not a
member of any assembly object definition, and is therefore only accessible via
normal parameter object access methods (i.e. explicit messaging).
Note that during I/O data exchanges, if the actual consumed data size is less
than or equal to a connection instance’s configured consumed connection size,
then all received data will be consumed and the connection will produce
normally. If the actual consumed data size is larger than the connection
instance’s configured consumed connection size, however, the consumed data
will be ignored and the connection will not produce.
The last I/O assembly configuration detail requiring discussion is the member
list definitions and the assignment of the offsets within each assembly
instance. Each assembly instance can be viewed as a contiguous array of
bytes, the size of which is dependent on the number of constituent member
parameters (6 bytes and 18 bytes, respectively, in our example). Including a
parameter in an assembly member list allows us to access that parameter via
I/O messaging, and is simply a function of assigning the parameter number to
an offset (an assembly object array starting position). Because all parameters
are 16-bit values, valid offsets range from 0, 2, 4...198. For example, after
defining our consumed data size for assembly instance 100 to be 6 bytes, the
initial (default) member list and related offset assignments will be as shown in
Table 5.
Table 5: Initial Example Assembly Instance Definition (Instance 100)
Offset Member Parameter Note
0 N/A
1
0
N/A
2 N/A
3
0
N/A
4 N/A
5
0
N/A
Note that the member parameter for each offset group is 0, which means “not
assigned”. If a 0 exists in an output (command) assembly member list, then
the consumed data in that position will be ignored. If a 0 exists in an input
(status) assembly member list, then the produced data in that position will
always be “0”.
For simplicity, we will assign our command-oriented parameters 1, 3 and 6 to
reside at output assembly instance offsets 0, 2 and 4, respectively. Any
arrangement of these three parameters within the three available member list
positions would be valid, however. After making these member list
assignments, the initial assembly object data array given in Table 5 is then
updated as indicated in Table 6 below: