Rockwell Automation SD3000 Drive Configuration, Programming - Manual (Page 79)

4.3 AutoMax Processor Task and UDC Task Coordination
Recall that all tasks running on AutoMax Processors have access to the UDC dual port registers, but
that UDC tasks can only access those common variables that represent registers in their own dual
port memory. Task coordination between the UDC module and the AutoMax Processor is generally
handled through periodic hardware interrupts generated by the UDC module. An AutoMax task
needs to define a hardware “event” that will trigger some action by an AutoMax task, using the
BASIC statement EVENT The EVENT statement must reference the hardware interrupt status and
control register ISCR% (register 2000 in the UDC dual port memory).
Although the UDC operating system itself actually causes the interrupt, a task in the rack (AutoMax or
UDC) must write to the scans per update register in the UDC dual port (register 2001) in order to
define the number of UDC task scans between updates of the the Nth scan application registers
(1300-1 599) and between hardware interrupts. See figure 3.2 for more information.
Note that the register values being latched on every Nth scan provide a consistent context for
evaluation of Control Block statements, but that BASIC statements in UDC tasks read and write data
immediately; that is, they do not read from and write to a local buffer. Referencing the same common
values in both Control Block and BASIC statements in one task can result in errors.
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