Omron CJ Series Operation Manual page 188

5 Operation
CPU Cycle
CIO Refresh
Output data refresh
Input data refresh
PROFIBUS Cycle
PROFIBUS DP I/O data exchange cycle > CPU cyclic refresh results in the following I/O transfer
characteristics.
• Not all output data is guaranteed to be transmitted over the PROFIBUS network (referring to
the figure above: Output data marked with "O" is overwritten by "O+1" and therefore lost).
• Input data is always sent to the CPU.
Note 1 CPU cyclic refresh times may vary, depending on the execution of the user program. If vari-
ation is too large, this may result in I/O data being lost.
2 To prevent output data not being transmitted over the PROFIBUS network the PROFIBUS
DP cycle time must made at least two times the CPU cyclic refresh time. This can be
accomplished by changing the Target Token Rotation time in the Master DTM Configura-
tion User Interface (see section 5-4-2 Setting the Bus Parameters).
 PROFIBUS DP Cycle < CPU Cyclic Refresh
The figure below shows the effects of the cyclic refresh rules for the case in which the PROFIBUS
DP I/O data exchange cycle < CPU cyclic refresh
5-36
Unit requests
cyclic refresh
Unit requests
cyclic refresh
Instruction Instruction
Execution Execution
O O+1
I
Cycle n
End of PROFIBUS DP cycle
CJ-series PROFIBUS Master Unit Operation Manual for NJ-series CPU Unit (W509)
Unit requests
cyclic refresh
Unit requests
cyclic refresh
Instruction Instruction
Execution Execution
O+2 O+3
I+1
Cycle n+1
End of PROFIBUS DP cycle
Unit requests
cyclic refresh
Instruction
Execution
O+4
I+2
Cycle n+2
End of PROFIBUS DP cycle