Mitsubishi MELSEC LJ71C24, User Manual

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11 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL
11.2 Sending Data to the External Device
This section explains the data transmission from the CPU module to an external device.
11.2.1 Transmission methods
The following shows the method of sending data to the external device through data
communication using the bidirectional protocol.
Sequence
program
Buffer memory
Transmission area
Transmission
completed
1)
Write
(BIDOUT
instruction)
External
device
(00
H
to FF
H
)
4)
(When abnormal)
2)
(When normal)
(00
H
to FF
H
)
Any data
3)
5)
Data
C24
Sum check code Data portion
Data length ENQ
ACK
NAK Error code
CPU module
BIDOUT instruction
completion device
BIDOUT instruction
CH1/CH2 Control timing
Send instruction
Contents
BIDOUT
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 C24 sends data by adding the control code ENQ at the beginning of the data.
When "Exist" is specified for "Sum check code" in Switch Setting of GX Works2,
the C24 adds the sum check code calculated by internal processing to the end
of the message and then transmits the message.
When "None" is specified in the Switch Setting of GX Works2, 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 C24.