Mitsubishi MELSEC LJ71C24, User Manual

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11 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL
11.4 Data Communications Precautions
The following shows the precautions when performing data communications using the
bidirectional protocol.
(1) When the transmission sequence is in the initial status, it indicates that data
transmission and reception processing has not been started.
The C24 transmission sequence is initialized in the following cases.
• The power is turned on, the CPU module is reset.
• When operating, or the mode is switched.
• When a response message (ACK, NAK, etc.) was received in reply to data
transmission.
• When a response message (ACK, NAK, etc.) was transmitted in reply to data
reception.
• When the CD(DCD) signal was turned off during data communications using
Check CD terminal in full-duplex communications through the RS-232 interface.
(2) As a data transmission procedure, data transmission from the external device or
the C24 should be performed after a response for the immediately preceding data
transmission has been received.
(3) Specify the same units of data length (words/bytes) of the messages to be
transmitted between an external device and the CPU module.
The CPU modules can be set using the GX Works2 word/byte units designation.
Make the length of the data area in the message to be transmitted and received
the size of the C24 buffer memory transmission data designation area and receive
data storage area, or less.
(4) NAK code response
1) Response from the C24 to external device
After the error detection message reception complete, it transmits the NAK
code to the external device.
2) Response from external device to the C24
Transmit the error code (0022
H
to 005F
H
) immediately after the NAK response.