Installation manual

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5
Software structure (continued)
Modicon TSX Micro
automation platform 0
PL7 Micro/Junior/Pro programming software
PL7 Micro/Junior/Pro software offers a Multitask software structure, consisting of:
b A master task (divided into sections, one of which may contain Grafcet).
b A fast task (divided into sections).
b One or more event-triggered tasks (only one section per task).
These tasks are independent and are executed in "parallel", with the PLC processor
managing the execution priority. When an event occurs, or at the start of the fast task
cycle:
b The current execution of lower priority tasks is stopped.
b The event-triggered task or the fast task is executed.
b The interrupted task takes over again when processing of the priority task is
completed
.
This structure can optimize use of the processing power, and can be used to
structure the application and simplify design and debugging, as it is possible to write
and debug each task independently of the others.
This compulsory task, which executes the main program, is periodic or cyclic (see
single task structures). It is activated systematically. It is intended for sequential
processing. Each section can be programmed in Ladder, Structured Text or
Instruction List language. One section is dedicated to Grafcet language; when this
language is chosen, 3 processing operations are proposed:
b Preliminary processing (PRE) is programmed in Ladder, Structured Text or
Instruction List language and processes initializations on power return, operating
mode modifications, input logic.
b Sequential processing (CHART) includes the graphic transcription and
management of Grafcet charts. It provides access to processing of the actions and
transition conditions.
b Post-processing (POST). This is programmed in Ladder, Structured Text or
Instruction List language and is used to process all the instructions from the
2 preceding processing operations and the indirect safety functions specific to the
outputs.
This task, which is higher priority than the master task, is periodic in order to leave
time for execution of the lower priority task. Processing operations in this task must be
as short as possible so as not to adversely affect the master task. It is useful when fast
periodic changes in discrete inputs need to be monitored.
Each section of this task can be programmed in Ladder, Structured Text or
Instruction List language.
Unlike the tasks described above, these tasks are not linked to a period. Their
execution is triggered by an event occurring in an application-specific module (eg.:
overrun of a counter threshold, change in state of a discrete input). These tasks have
higher priority than all other tasks, and they are therefore suitable for processing
operations requiring very short response times to the occurrence of an event.
They can be programmed in Ladder, Structured Text or Instruction List language.
Number of EVTi control events:
b TSX Micro PLCs: 8 events with TSX 37 10 and 16 events with TSX 37 21/22.
b Premium PLCs: 32 events with TSX 57 10 and 64 events with TSX 57 20/30/40
and PCX 57 20/30.
TSX Micro TSX 37 21/22 and Premium PLCs have 2 priority levels (EVT0 event has
priority over other EVTi events).
Multitask software structure
SR0
Master taskFast task
Event triggered tasks
SR0
Priority + ... –
Alarm_Sas(LD)
Safety_Mon(LD)
Alarm_Furnace(ST)
Alarm_Cleaning(ST)
Sas(LD)
Furnace_1(LD)
Drying(LD)
PRE(LD)
CHART
POST(IL)
Master task
Fast task
Event triggered tasks
P
resentation:
p
age 5/5
Functions:
pages 5/12 to 5/15
Characteristics:
pages 5/16 to 5/18
Reference:
pages 5/18 to 5/19
Courtesy of Steven Engineering, Inc. ● 230 Ryan Way, South San Francisco, CA 94080-6370 ● General Inquiries: [phone] ● www.stevenengineering.com
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