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CHAPTER3 CPU MODULE OPERATION
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3.8 I/O Processing and Response Delay
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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( Section 3.8.1)
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( Section 3.8.2)
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.
Tabl e3. 3
shows the availability of the refresh mode and the direct mode for each input and output.
Table3.3 Availability of modes
Item Refresh mode direct mode
Input/output modules
Available Available
Input/output of intelligent function modules
Remote input/output in CC-Link IE controller network, MELSECNET/H, or CC-Link Available Not available