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Maximum Transmission Delays: Writing/Reading to CPU Unit Section 7-5
7-5 Maximum Transmission Delays: Writing/Reading to CPU
Unit
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.
Write Command
Delay Time
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.)
Receive Processing
(Command)
Number of words sent
× 0.003 + 0.704 ms
CPU Bus Unit Service
Cycle
The processing time will be as follows, depending on the CPU processing
mode settings at the CPU Unit.
For details, refer to the CPU Unit operation manual.
CPU Bus Unit Service
Processing Time
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.
Baud rate Delay time
100Base-TX
Number of words sent × 0.0013 + 0.0118 ms
10Base-TX
Number of words sent × 0.0019 + 0.0157 ms
CPU execution mode Processing time considerations
Normal Mode CPU Unit cycle time
Priority peripheral ser-
vicing
Ethernet Unit is given prior-
ity.
Time slice instruction execu-
tion time
Ethernet Unit is not given
priority.
CPU Unit cycle time
Parallel processing with
synchronous memory
access
CPU Unit cycle time
Parallel processing with
asynchronous memory
access
0.2 ms + peripheral servicing time (1 ms max. of peripheral
servicing time for each Special I/O Unit, CPU Bus Unit,
peripheral port, RS-232C port, and Inner Board)
CPU execution mode Processing time considerations
Normal Mode Set time for peripheral servicing
(Default: 4% of CPU Unit cycle time)
Priority peripheral ser-
vicing
Priority given to Ethernet
Unit
Time slice peripheral servic-
ing execution time
Priority not given to Ethernet
Unit
Set peripheral servicing time
(Default: 4% of CPU Unit
cycle time)