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CPU Bus Unit Area Section 4-5
4-5 CPU Bus Unit Area
The CPU Bus Unit Area contains 400 words with addresses ranging from
CIO 1500 to CIO 1899. Words in the CPU Bus Unit Area can be allocated to
CPU Bus Units to transfer data such as the operating status of the Unit. Each
Unit is allocated 25 words based on the Unit’s unit number setting.
Data is exchanged with CPU Bus Units once each cycle during I/O refreshing,
which occurs after program execution. (Words in this data area cannot be
refreshed with immediate-refreshing or IORF(097).)
Each CPU Bus Unit is allocated 25 words based on its unit number, as shown
in the following table.
The function of the 25 words depends upon the CPU Bus Unit being used. For
details, refer to the Unit’s operation manual.
Words in the CPU Bus Unit Area that aren’t allocated to CPU Bus Units can
be used in programming.
Forcing Bit Status Bits in the CPU Bus Unit Area can be force-set and force-reset.
CPU Bus Unit Area
Initialization
The contents of the CPU Bus Unit 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 and the IOM Hold Bit is OFF or not protected in
the PLC Setup
3. When the CPU Bus Unit 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 CPU Bus Unit Area will be re-
tained when FALS(007) is executed.)
Unit
number
Allocated words Unit
number
Allocated words
0 CIO 1500 to CIO 1524 8 CIO 1700 to CIO 1724
1 CIO 1525 to CIO 1549 9 CIO 1725 to CIO 1749
2 CIO 1550 to CIO 1574 A CIO 1750 to CIO 1774
3 CIO 1575 to CIO 1599 B CIO 1775 to CIO 1799
4 CIO 1600 to CIO 1624 C CIO 1800 to CIO 1824
5 CIO 1625 to CIO 1649 D CIO 1825 to CIO 1849
6 CIO 1650 to CIO 1674 E CIO 1850 to CIO 1874
7 CIO 1675 to CIO 1699 F CIO 1875 to CIO 1899
CPU Bus Unit Area
(25 words/Unit)
CPU Bus UnitCPU Unit
I/O
refreshing
CPU Bus Unit
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