Omron CP1H CPU UNITS - PROGRAMMING 05-2007, Operation Manual

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Internal I/O Area
Section 4-9
4-9 Internal I/O Area
The Internal I/O (Work) Area contains 512 words with addresses ranging from
W0 to W511. These words can be used in programming as work words.
There are unused words in the CIO Area (CIO 1200 to CIO 1499 and
CIO 3800 to CIO 6143) that can also be used in the program, but use any
available words in the Work Area first because the unused words in the CIO
Area may be allocated to other applications when functions are expanded.
Forcing Bit Status Bits in the Work Area can be force-set and force-reset.
Work Area Initialization The contents of the Work Area will be cleared in the following cases:
1. When the operating mode is changed from PROGRAM to RUN or MONI-
TOR mode or vice-versa and the IOM Hold Bit is OFF
2. When the power is cycled
3. When the Work Area is cleared from the CX-Programmer.
4. When PLC operation is stopped when a fatal error other than an
FALS(007) error occurs. (The contents of the Work Area will be retained
when FALS(007) is executed.)
4-10 Holding Area (H)
The Holding Area contains 512 words with addresses ranging from H0 to
H511 (bits H0.00 to H511.15). These words can be used in programming.
Holding Area Initialization Data in the Holding Area is not cleared when the power is cycled or the PLC’s
operating mode is changed from PROGRAM mode to RUN or MONITOR
mode or vice-versa.
A Holding Area bit will be cleared if it is programmed between IL(002) and
ILC(003) and the execution condition for IL(002) is OFF. To keep a bit ON
even when the execution condition for IL(002) is OFF, turn ON the bit with the
SET instruction just before IL(002).
Self-maintaining Bits When a self-maintaining bit is programmed with a Holding Area bit, the self-
maintaining bit won’t be cleared even when the power is reset.
Note 1. If a Holding Area bit is not used for the self-maintaining bit, the bit will be
turned OFF and the self-maintaining bit will be cleared when the power is
reset.
2. If a Holding Area bit is used but not programmed as a self-maintaining bit
as in the following diagram, the bit will be turned OFF by execution condi-
tion A when the power is reset.
3. H512 to H1535 are used as a Function Block Holding Area. These words
can be used only for function block instances (internally allocated variable
H0.00
H0.00
A
H0.00