7 DATA COMMUNICATIONS USING BIDIRECTIONAL PROTOCOL
7.2 Sending Data to the External Device
This section explains data transmission from the PLC CPU to the external device.
7.2.1 Transmission methods
The following shows the method of sending data to the external device through data communication using the bidirectional protocol.
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PLC program |
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| Transmission area |
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Write | Data |
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| Sum check code |
| Data portion Data length | ENQ |
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(BIDOUT |
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instruction) | (00H to FFH) |
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| ACK |
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| Transmission |
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Contents | CH1/CH2 | Control timing |
Send instruction
BIDOUT instruction completion device
BIDOUT instruction |
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| BIDOUT |
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1)Data such as control data and transmission data are stored in the device designated with the BIDOUT instruction and then the BIDOUT instruction is executed.
2)The transmission data count and transmission data are written into the transmission area of the buffer memory.
3)The Q series C24 sends data by adding the control code ENQ at the beginning of the data.
When "Sum check" is designated with GX Developer, the Q series C24 adds the sum check code calculated by internal processing to the end of the message and then transmits the message.
When "No sum check" is designated with GX Developer, no sum check code is sent.
4)A response for the data transmission (for normal completion: ACK message; for
abnormal completion: NAK message) is received.
5)The execution of the BIDOUT instruction completes with the transmission processing completion of the Q series C24.
7 - 15 | 7 - 15 |