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3.8
I/O Processing and Response Delay
The CPU module performs I/O processing in the refresh mode.
Using the direct access input/output in a sequence program, however, allows the CPU module to perform
I/O processing in the direct mode at the time of each instruction execution.
This section describes these I/O processing modes of the CPU module and response delays.
(a)
Refresh mode(
Refresh mode is a mode for the CPU module to access input/output modules and perform I/O
processing collectively before the start of sequence program operations.
(b)
Direct mode(
Direct mode is a mode for the CPU module to access input/output modules and perform I/O
processing at the timing when each instruction is executed in a sequence program.
To access input/output modules in the direct mode, use the direct access input or direct access
output in a sequence program.
(1) Differences between refresh mode and direct mode
The direct mode directly accesses input/output modules at execution of an instruction. Therefore, data
input is faster than in refresh mode.
Processing time required for each instruction, however, is longer.
shows the availability of the refresh mode and the direct mode for each input and output.
Table3.3
Input/output modules
Input/output of intelligent function modules
Remote input/output in CC-Link IE controller network, MELSECNET/H, or CC-Link
Section 3.8.1)
Section 3.8.2)
Table3.3 Availability of modes
Item
CHAPTER3 CPU MODULE OPERATION
Refresh mode
direct mode
Available
Available
Available
Not available
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