Rockwell Automation 1760-xxxx Pico GFX-70 Controllers User Manual - Manual (Page 356)

Publication 1760-UM002B-EN-P - March 2005
8-2 Inside Pico GFX-70
Evaluating Function Blocks
• process the function blocks which are used: the output data of a
function block is updated immediately after processing. Pico GFX-70
processes the function blocks according to the function block list (see
Calling the Function Blocks via the FUNCTION RELAYS Menu on page
4-29) from top to bottom. You can sort the function block list with
PicoSoft Pro. You can then, for example, use the results consecutively.
• establish contact to the “outside world”: The output relays Q 01 to Q
(S).. are switched and the inputs I1 to I (R).. are read once more.
• Pico GFX-70 also copies all the new switching states to the status image
register.
• exchange all data on the Pico-Link network (read and write).
Pico GFX-70 only uses this status image for one cycle. This ensures that each
circuit connection is evaluated with the same switching states for one cycle,
even if the input signals I1 to I12 change their status several times within a
cycle.
Serial Interface Data Access During the Program Cycle
The data exchange with the point-to-point connection can be carried out in
any segment of the program cycle. This data exchange increases the cycle time
with both active and remote stations. Only use data that is absolutely necessary.
Loading Visualization Data
When setting a program to RUN that contains visualization data, the contents
of the screens to be displayed have to be loaded. This operation is repeated
every 200 ms. With large screens this can take up to one millisecond of cycle
time.
The time required for loading in the event of a screen change depends on the
size of the screens to be loaded. During a screen change, the new screen is
loaded from the screen memory into the RAM.
The loading time can be calculated as follows:
screen size in byte multiplied by 80 µs.
IMPORTANT
The following must be observed when operating a PID
controller function block.
The cycle time of the program must be less than the scan
time of the controller. If the cycle time is greater than the
controller scan time, the controller will not be able to
achieve constant results.