PC Control / Profi Control 645-12M Instruction Manual pdf - Kuhnke
PC Control / Profi Control 645-12M Instruction Manual pdf - Kuhnke PC Control / Profi Control 645-12M Instruction Manual pdf - Kuhnke
4.9.1. Data consistency secured by OS_CRIT Kuhnke controller such as PC Control 645-12M have an operating system with multi-tasking capability. Tasks such as processing the user program or PROFIBUS communication are acyclically arranged. Task changes are timer controlled, i.e. they do not relate to the processing step of the preceding task. This may lead to the PROFIBUS task updating the process image between two user program commands. Consequently, the external operands read after the next user program command are more up-to-date than the data read previously. This may cause problems if the different bits of information are functionally related, because misinterpretations cannot be excluded in this case. Just imagine a 24-bit analogue value supplied by a positioning slave that is to be read by two commands, and then there is a task change right between the two reading processes. The interpretation of the analogue value might deliver an entirely wrong result. KUBES module OS_CRIT remedies this situation by influencing the operating system to prevent task changes within limited user program sections. OS_CRIT is delivered with the KUBES program package. A constant value is specified as its starting parameter. Example Prevent task change (constant = 1) JPK OS_CRIT , _____ 1 -|_____|- LD BI01a00. ; low word =D BM00.00 LD BI01a02. ; high word =D BM00.02 Allow task change (constant = 0) JPK OS_CRIT , _____ 0 -|_____|- 4 - 46
PC Control 645-12M on PROFIBUS PROFIBUS data is consistent between the two load commands. In our example, the "low word" and "high word" values are therefore ensured to be updated by PROFIBUS at the same time. OS_CRIT only secures the consistency of I/O data that has been marked as consistent in the DP slave's GSD file. OS_CRIT directly influences the operating system. You are therefore requested to obey the following rules: 1. Always start OS_CRIT in pairs (first using constant 1, then constant 0). 2. Keep the program section between the two module start commands as small as possible. 3. The program section delimited by OS_CRIT must not contain a call for another module. This call command would terminate data consistency by re-enabling task changes. 4 - 47
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<strong>PC</strong> <strong>Control</strong> <strong>645</strong>-<strong>12M</strong> on PROFIBUS<br />
PROFIBUS data is consistent between the two load commands.<br />
In our example, the "low word" and "high word"<br />
values are therefore ensured to be updated by PROFIBUS<br />
at the same time.<br />
OS_CRIT only secures the consistency of I/O data that has<br />
been marked as consistent in the DP slave's GSD file.<br />
OS_CRIT directly influences the operating system. You are<br />
therefore requested to obey the following rules:<br />
1. Always start OS_CRIT in pairs (first using constant 1,<br />
then constant 0).<br />
2. Keep the program section between the two module start<br />
commands as small as possible.<br />
3. The program section delimited by OS_CRIT must not<br />
contain a call for another module. This call command<br />
would terminate data consistency by re-enabling task<br />
changes.<br />
4 - 47
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