Omron CJ1W-CT021 Operation Manual page 139

IORD-Instruction Section 4-4
Unit is ready to execute the IORD-instruction. If an error occurs during the execu-
tion of the IORD-instruction the ER-flag turns ON.
Note If you omit to include the Data Transfer Busy bit (CIO n+19, bit 02) in the ladder
instruction and you start issuing an IORD-instruction while another IOWR/IORD-
instruction is in progress the ER-flag turns ON. Therefore, to guarantee correct
execution of IORD-instructions, you should always use the ladder diagram struc-
ture as shown above.
The response time for bits allocated to outputs (e.g., Open Gate Bit) will be
delayed while the Data Transfer Busy bit (CIO n+19, bit 02) is ON (e.g., when time
is required to process IORD or when a Unit is reset). In any case, the bit allocated
to the output will be processed as soon as the Data Transfer Busy bit turns OFF.
Comparison stops while the Data Transfer Busy bit (CIO n+19, bit 02) is ON. Refer
to 3-5-1-2 "Configuration and operation in Range Mode" and 3-5-2-2 "Configura-
tion and operation in Comparison Mode" for details.
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