Rockwell Automation SA500 Drive Configuration and Programming - Manual (Page 94)

4-8 SA500 Drive Configuration and Programming
same time base for task execution. Note that all UDC modules in a rack are not
required to have the same value in the TICKS parameter of the SCAN_LOOP block in
both their tasks. In other words, if the UDC module in slot 6 has TICKS = 10 in its
tasks, and the UDC module in slot 7 has TICKS = 20 in its tasks, the tasks on the UDC
module in slot 6 will execute twice as often as the tasks on the UDC module in slot 7,
but they will execute on the same time basis, i.e., time zero is determined by CCLK
timer expiration.
As soon as the UDC module and PMI are connected over the fiber-optic link, the PMI
will request its operating system from the UDC module. Recall that the PMI operating
system is part of the UDC operating system. As long as the UDC module has its own
operating system and parameter object file, it will download to the PMI the correct
operating system.
In order for the PMI and the UDC module to be synchronized, the UDC module must
have its operating system, parameter object file, and configuration loaded. In addition,
CCLK must be turned on in the AutoMax rack.
If the UDC tasks are already loaded onto the UDC module when the PMI requests its
operating system, the UDC module will also send information about when the PMI
should send feedback register data required by the UDC task(s). This ensures that the
data is measured or calculated as close as possible to the time it is needed in order to
ensure it is as current as possible for the next scan of the UDC task(s).
The UDC operating system determines the feedback register message timing required
by examining the SCAN_LOOP block in each UDC task so that the feedback will arrive
at the UDC module just before it is needed. For example, if the TICKS parameter
value in the SCAN_LOOP block were 10, feedback data would be needed by the UDC
module immediately before 10 x 500
At first, when the UDC module and PMI(s) are powered up and connected via the
fiber-optic link, their system clocks are not synchronized. In order for the PMI and
UDC module to be synchronized to the same clock signal for communicating
command and feedback data on a regular and predictable basis, an AutoMax task
must turn on the CCLK signal in the rack. Until CCLK is turned on, command and
feedback messages are sent periodically, but not on a predictable basis.
CCLK can be turned on by setting the appropriate bit in UDC register 2000 (the
interrupt status and control register for both A and B drive tasks), or by setting a bit in
another module that can turn on CCLK. Only one module in the rack must turn on
CCLK. Note that after a STOP ALL occurs in the rack, CCLK will be disabled and must
be re-enabled again in order for UDC tasks to go into run. See figure 4.2 for the typical
data flow between the UDC module and the PMI.
To verify that communication between the UDC module and the PMI is resulting in
up-to-date feedback data, it is recommended that the drive’s run permissive logic
include the CCLK synchronized status bit (register 200/1200, bit 14, CCLK_OK@)
and the communication lost fault bit (register 202/1202, bit 15, FLT_COM@) as shown
in figure 4.2.