Automation Direct DirectLogic Series Application Note - Page 3
Browse online or download pdf Application Note for Controller Automation Direct DirectLogic Series. Automation Direct DirectLogic Series 5 pages. Plc
Print Page2) When the stage bit is transitioning from on to off, the corresponding stage will be scanned one more
time to turn off all outputs that are currently on.
3) When the stage bit is off, the
corresponding stage is not scanned and therefore no logic in that stage is
evaluated or processed.
There are some caveats to be aware of with stage programming that concern turning stages on and off.
These are detailed in AutomationDirect PLC user manuals, which can be purchased separately or
downloaded from www.automationdirect.com.
Stage programming can save PLC memory and improve scan time by reducing the number of repeated
sequences and by scanning only the stages that are active. These are two more good reasons to think
about using stage programming, but they are not good reasons to use stage if the process is not suited
for it.
Stage programming and standard RLL logic style programming can be intermixed by placing standard
RLL at the beginning of the program, but usually there is no need to do this. A proper stage program will
start with one or more initial stages and have numerous stages that will be turned on and off throughout
the program cycle.
There are two ways to activate a stage: with a "Jump" instruction or by setting the stage bit. The Jump
instruction deactivates the current stage while activating the specified stage. It does not jump over other
code.
Setting the stage bit will activate the specified stage while leaving the current stage running as well. By
using Set instructions you can have many stages active at one time.
The Reset instruction works in much the same manner as the Set instruction. You can reset one stage or
a whole group of stages at one time using the Reset instruction.
When exiting a stage, whether by jumping out of it or by resetting the stage bit, the stage will always finish
scanning before turning the power rail off. When jumping out of the current stage, the current stage will be
scanned one more time after the current scan is completed. This behavior can cause problems with some
processes if it is not accounted for.
A stage is turned off by jumping out of it or by resetting it. All outputs, timers and counters, unless set, will
be turned off. The simple explanation is that turning off a stage turns off the power rail. If there is no
power, then the instructions are turned off. Timers and Out instructions, for example, rely on the power
rail to maintain their state. Once power is removed, they turn off. This happens with other instructions as
well. The following examples show Stage programming and how Stage would look if using Standard RLL:
THIS INFORMATION PROVIDED BY AUTOMATIONDIRECT.COM TECHNICAL SUPPORT
IS PROVIDED "AS IS" WITHOUT A GUARANTEE OF ANY KIND.
These documents are provided by our technical support department to assist others. We do not guarantee
that the data is suitable for your particular application, nor do we assume any responsibility for them in
your application.
Page 3 of 5