Index Registers - Omron CP1H-X40D Operation Manual

Index Registers

4-15 Index Registers

Indirect Addressing
172
CPU Bus Units (D30000 to D31599)
Each CPU Bus Unit is allocated 100 words (based on unit numbers 0 to F).
Refer to the Unit's operation manual for details on the function of these words.
With some CPU Bus Units such as Ethernet Units, initial settings must be reg-
istered in the CPU Unit's Parameter Area; this data can be registered with the
CX-Programmer.
DM Area for CPU Bus Units
(100 words/Unit)
■ DM Fixed Allocation Words for Modbus-RTU Easy Master
The following DM area words are used as command and response storage
areas for the Modbus-RTU Easy Master function.
D32200 to D32299: Serial port 1
D32300 to D32399: Serial port 2
For use of these areas, refer to 6-1-3 Modbus-RTU Easy Master Function.
The sixteen Index Registers (IR0 to IR15) are used for indirect addressing.
Each Index Register can hold a single PLC memory address, which is the
absolute memory address of a word in I/O memory. Use MOVR(560) to con-
vert a regular data area address to its equivalent PLC memory address and
write that value to the specified Index Register. (Use MOVRW(561) to set the
PLC memory address of a timer/counter PV in an Index Register.)
Note Refer to Appendix E Memory Map for more details on PLC memory
addresses.
When an Index Register is used as an operand with a "," prefix, the instruction
will operate on the word indicated by the PLC memory address in the Index
Register, not the Index Register itself. Basically, the Index Registers are I/O
memory pointers.
• All addresses in I/O memory (except Index Registers, Data Registers, and
Condition Flags) can be specified seamlessly with PLC memory
addresses. It isn't necessary to specify the data area. I/O memory
addresses for IR, DR, and Condition Flags, however, cannot be held.
• In addition to basic indirect addressing, the PLC memory address in an
Index Register can be offset with a constant or Data Register, auto-incre-
mented, or auto-decremented. These functions can be used in loops to
read or write data while incrementing or decrementing the address by one
each time that the instruction is executed.
Special I/O Unit
CPU Unit
Data trans-
ferred to the
CJ Unit when
the PLC is
turned ON or
the Unit is
restarted.
Data trans-
ferred to the
CPU Unit at
cyclic refresh-
ing or when
necessary.
Section 4-15