Omron CS1D DUPLEX SYSTEM - 10-2009 Operation Manual page 297

I/O Area
I/O Area Initialization
1,2,3...
IOM Hold Bit Operation
Input Bits
Normal I/O Refreshing
the first Rack word with any Programming Device other than a Programming
Console. The maximum number of bits that can be allocated for external I/O
will still be 5,120 (320 words) even if the I/O Area is expanded.
Note The maximum number of external I/O points depends upon the CPU Unit
being used.
Words in the I/O Area are allocated to I/O terminals on Basic I/O Units.
Words are allocated to Basic I/O Units based on the slot position (left to right)
and number of words required. The words are allocated consecutively and
empty slots are skipped. Words in the I/O Area that aren't allocated to Basic
I/O Units can be used only in the program.
Bits in the I/O Area can be force-set and force-reset.
The contents of the I/O Area will be cleared in the following cases:
1. The operating mode is changed from PROGRAM to RUN or MONITOR
mode or vice-versa and the IOM Hold Bit is OFF.
(See the following explanation of IOM Hold Bit Operation.)
2. The PLC's power supply is cycled and the IOM Hold Bit is OFF or not pro-
tected in the PLC Setup.
(See the following explanation of IOM Hold Bit Operation.)
3. The I/O Area is cleared from a Programming Device.
4. PLC operation is stopped when a fatal error other than an FALS(007) error
occurs. (The contents of the I/O Area will be retained if FALS(007) is exe-
cuted.)
By default, the I/O Area is cleared when power is interrupted or the CPU Unit
is restarted.
If the IOM Hold Bit (A50012) is ON, the contents of the I/O Area won't be
cleared when a fatal error occurs or the operating mode is changed from
PROGRAM mode to RUN or MONITOR mode or vice-versa.
If the IOM Hold BIt (A50012) is ON and the PLC Setup's "IOM Hold Bit Status
at Startup" setting is set to protect the IOM Hold Bit, the contents of the I/O
Area won't be cleared when the PLC's power supply is cycled. All I/O bits,
including outputs, will retain the status that they had before the PLC was
turned off.
Note If the I/O Hold Bit is turned ON, the outputs from the PLC will not be turned
OFF and will maintain their previous status when the PLC is switched from
RUN or MONITOR mode to PROGRAM mode. Make sure that the external
loads will not produce dangerous conditions when this occurs. (When opera-
tion stops for a fatal error, including those produced with the FALS(007)
instruction, all outputs from Output Unit will be turned OFF and only the inter-
nal output status will be maintained.)
A bit in the I/O Area is called an input bit when it is allocated to an Input Unit.
Input bits reflect the ON/OFF status of devices such as push-button switches,
limit switches, and photoelectric switches. There are two ways for the status of
input points to be refreshed in the PLC: normal I/O refreshing and IORF(097)
refreshing.
The status of I/O points on external devices is read once each cycle after pro-
gram execution.
Section 8-3
261