170
Index Registers Section 4-15
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 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.
4-15 Index Registers
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.
Indirect Addressing 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.
DM Area for CPU Bus Units
(100 words/Unit)
CPU Unit
Special I/O 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.
To Next Page
Loading...
Need help?
General
