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4. CPU MODULE
4.1.1 Overview of operation processing
An overview of processing when starting power supply for the CPU module to execution of
the sequence program is explained.
CPU modules processing may be categorized roughly into the following four kinds:
(1) Initial processing
This is a preprocess to execute sequence operations, and is performed only once
upon power-on or reset.
(a) Resets the I/O module and initialize it.
(b) Initializes the range of data memory for which latch is not set up (sets the bit
device to OFF and the word device to 0).
(c) Allocates I/O address of the I/O module automatically based on the I/O module
number or the position of installation on the extension base unit.
(d) Execute the self-diagnostics check for the parameter setting and the operation
circuit. (Refer to Section 4.1.4)
(e) For the control station of the MELSECNET/10 or the master station of
MELSECNET (II)/B, sets the network/link parameter information to the network/
data-link module, and commences the network communication/data link.
(2) Refresh processing of I/O module
Executes the refresh processing of I/O module.
(Refer to the ACPU/QCPU-A (A Mode) Programming Manual (Fundamentals).)
(3) Operation processing of a sequence program
Executes the sequence program from step 0 to the END instruction written in the
programmable controller CPU.
(4) END processing
This is a post-process to finish one cycle of operation processing of the sequence
program and to return the execution of the sequence program to the step 0.
(a) Executes self-diagnosis checks, such as a fuse blown, a module verify, and a
low battery.
(Refer to Section 4.1.4)
(b) Updates the current value of the timer, sets the contact ON/OFF, updates the
current value of the counter and sets the contact to ON.
(Refer to the ACPU/QCPU-A (A Mode) Programming Manual (Fundamentals).)
(c) Executes the data exchange between the programmable controller CPU and a
computer link module (e.g.A1SJ71UC24-R2), when there is a data read or write
request from the computer link module.
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