Controller memory constraints on simultaneous event generation

Controller memory constraints limit the number of events that can be generated at one time. Consider these points to help plan to configure sequences that execute within the constraints of the controller:
  • Multiple Parameter Value Update events generate when:
    • A sequence is started, generates one event to record the initial value of each Sequencing Input Parameter.
    • A sequence changes state to COMPLETE, STOPPED, or ABORTED generates one event to record each sequence output parameter updated.
  • Multiple Step Input and Output Tag Value events generates when:
    • A step becomes active prior to running, generates one event to record each step input tag value passed from the sequence to a phase input parameter.
    • A step changes state to COMPLETE, STOPPED, or ABORTED generates one event to record each step output tag updated from a phase output parameter.
    • Each sequence program has four event packets for sequence input parameters and four event packets for sequence output parameters.
    • Each step has two event packets for step input tags and two event packets for step output tags.
    • SEQ_BOOL: 7 bytes
    • SEQ_SINT: 7 bytes
    • SEQ_INT: 8 types
    • SEQ_DINT: 10 bytes
    • SEQ_REAL: 10 bytes
    • SEQ_STRING: 94 bytes.
The number of events that can be generated is dependent on the number of dedicated event packets and when multiple packets are used, how the events are loaded into the packet. The size of the event depends on the data type of the value being reported. Each event packet contains 419 bytes:
Calculate the size required of each packet by multiplying the number of Sequence Parameters or Step Tag events to be generated to record changes in value:
Example 1: An
Equipment Sequence
 has six SEQ_REAL and three SEQ_STRING input parameters
When an
Equipment Sequence
 has six SEQ_REAL and three SEQ_STRING I\input parameters, the initialization events will be generated to record the initial value of each Sequence Input parameter.
  • The six SEQ_REAL input parameters will require 6 * 10, or 60 bytes.
  • The three SEQ_STRING input parameters will require 3 * 94, or 282 bytes.
  • One event packet can hold all nine initialization events, so this configuration is within specifications.
Example 2: A step has eight SEQ_STRING and five SEQ_REAL Step Input Tags
When the Step becomes active, 12 events, totaling 802 bytes, must be generated to record the input values passed to the phase.
  • The first event packet is loaded with four SEQ_STRING events, requiring 4 * 94, or 376 bytes. The next event to load is 94 bytes and won’t fit. The second event packet must be used.
  • The second event packet is loaded with four more SEQ_STRING events, totaling 376 bytes. The next four SEQ_REAL events consume 40 more bytes, totaling 416 bytes. There is no more room in the second event packet for the data for the fifth SEQ_REAL step input tag.
  • The two dedicated event packets do not hold all 12 events, so this is a configuration error.
Provide Feedback
Have questions or feedback about this documentation? Please submit your feedback here.