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Overview of I/O Memory Area Section 4-1
Counter PVs
The PVs are read and written as words (16 bits). The PVs count up or down
as the counter operates.
Condition Flags These flags include the Arithmetic Flags, such as the Error Flag and Equals
Flag, which indicate the results of instruction execution as well as the Always
ON and Always OFF Flags. The Condition Flags are specified with symbols
rather than addresses.
Clock Pulses The Clock Pulses are turned ON and OFF by the CPU Unit’s internal timer.
These bits are specified with symbols rather than addresses.
Task Flag Area (TK) A Task Flag will be ON when the corresponding cyclic task is in executable
(RUN) status and OFF when the cyclic task hasn’t been executed (INI) or is in
standby (WAIT) status.
Index Registers (IR) Index registers (IR0 to IR15) are used to store PLC memory addresses (i.e.,
absolute memory addresses in RAM) to indirectly address words in I/O mem-
ory. The Index Registers can be used separately in each task or they can be
shared by all tasks.
Data Registers (DR) Data registers (DR0 to DR15) are used together with Index Registers. When a
Data Register is input just before an Index Register, the content of the Data
Register is added to the PLC memory address in the Index Register to offset
that address. The Data Registers can be used separately in each task or they
can be shared by all tasks.
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