432
Index Registers Section 9-17
Index Register
Initialization
The Index Registers will be cleared in the following cases:
1,2,3... 1. The operating mode is changed from PROGRAM mode to RUN/MONITOR
mode or vice-versa and the IOM Hold Bit is OFF.
2. The PLC’s power supply is cycled and the IOM Hold Bit is OFF or not pro-
tected in the PLC Setup.
IOM Hold Bit Operation If the IOM Hold BIt (A50012) is ON, the Index Registers won’t be cleared
when a FALS error occurs or the operating mode is changed from PROGRAM
mode to RUN/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 Index Registers won’t
be cleared when the PLC’s power supply is reset (ON
→ OFF → ON).
Precautions Do not use Index Registers until a PLC memory address has been set in the
register. The pointer operation will be unreliable if the registers are used with-
out setting their values.
The values in Index Registers are unpredictable at the start of an interrupt
task. When an Index Register will be used in an interrupt task, always set a
PLC memory address in the Index Register with MOVR(560) or MOVRW(561)
before using the register in that task.
Each Index Register task is processed independently, so they do not affect
each other. For example, IR0 used in Task 1 and IR0 used in Task 2 are differ-
ent. Consequently, each Index Register task has 16 Index Registers.
Limitations when Using Index Registers
• It is only possible to read the Index Register for the last task executed
within the cycle from the Programming Devices (CX-Programmer or Pro-
gramming Console). If using Index Registers with the same number to
perform multiple tasks, it is only possible with the Programming Devices
to read the Index Register value for the last task performed within the
cycle from the multiple tasks. Nor is it possible to write the Index Register
value from the Programming Devices.
• It is not possible to either read or write to the Index Registers using Host
Link commands or FINS commands.
• The Index Registers cannot be shared between tasks for CJ1 CPU Units.
(With CJ1-H and CJ1M CPU Units, a PLC Setup setting can be made
from the CX-Programmer to share Index Registers between tasks.)
Monitoring Index Registers
It is possible to monitor Index Registers as follows:
To use the Programming Devices to monitor the final Index Register values for
each task, or to monitor the Index Register values using Host Link commands
or FINS commands, write a program to store Index Register values from each
task to another area (e.g., DM area) at the end of each task, and to read Index
Register values from the storage words (e.g., DM area) at the beginning of
each task. The values stored for each task in other areas (e.g., DM area) can
then be edited using the Programming Devices, Host Link commands, or
FINS commands.
To Next Page
Loading...
