Maximum Transmission Delays: Writing/Reading to CPU Unit | Section |
7-5 Maximum Transmission Delays: Writing/Reading to CPU Unit
Write Command Delay Time
The time for the response to be received after a remote node on the Ethernet network sends a memory area read or write command to a PLC can be calcu- lated using the following formula.
Maximum transmission delay =
Transmission processing time (remote node)
+Transmission delays
+Reception processing time (command) (local node)
+CPU Bus Unit service cycle (local node)
+CPU Bus Unit service processing time (local node)
+Transmission processing time (response) (local node)
+Transmission delays
+Reception processing time (remote node)
Transmission Delay | The transmission delay time depends on the baud rate set for the Ethernet | ||
| Unit, as shown in the following table. (Additional delays may depending on | ||
| devices, such as hubs, in the network configuration.) | ||
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| Baud rate | Delay time |
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| Number of words sent ⋅ 0.0013 + 0.0118 ms |
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| Number of words sent ⋅ 0.0019 + 0.0157 ms |
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Receive Processing (Command)
CPU Bus Unit Service Cycle
Number of words sent ⋅ 0.003 + 0.704 ms
The processing time will be as follows, depending on the CPU processing mode settings at the CPU Unit.
CPU execution mode | Processing time considerations | |
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Normal Mode | CPU Unit cycle time |
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Priority peripheral ser- | Ethernet Unit is given prior- | Time slice instruction execu- |
vicing | ity. | tion time |
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| Ethernet Unit is not given | CPU Unit cycle time |
| priority. |
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Parallel processing with | CPU Unit cycle time |
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synchronous memory |
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access |
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Parallel processing with | 0.2 ms + peripheral servicing time (1 ms max. of peripheral | |
asynchronous memory | servicing time for each Special I/O Unit, CPU Bus Unit, | |
access | peripheral port, | |
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CPU Bus Unit Service Processing Time
For details, refer to the CPU Unit operation manual.
The CPU Bus Unit service processing time is determined according to the CPU execution processing mode at the CPU Unit, as shown in the following table.
CPU execution mode | Processing time considerations | |
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Normal Mode | Set time for peripheral servicing | |
| (Default: 4% of CPU Unit cycle time) | |
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Priority peripheral ser- | Priority given to Ethernet | Time slice peripheral servic- |
vicing | Unit | ing execution time |
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| Priority not given to Ethernet | Set peripheral servicing time |
| Unit | (Default: 4% of CPU Unit |
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| cycle time) |
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