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4 MESSAGES OF SERIAL COMMUNICATION MODULE
4.3 Details of Setting Data
4.3 Details of Setting Data
This section explains how to specify the common data items and their content in each message.
Control code
Control code is a data that has special meaning (such as head data of a message) for C24 transmission control.
Control code used in a message (format 1 to format 4) in ASCII code
The control code used for a message in ASCII code (format 1 to format 4) is shown in the following table.
■EOT(04H), CL(0CH)
EOT and CL are codes for initializing the transmission sequence for data communications in ASCII code using the MC
protocol and for placing C24 into wait state to receive commands from an external device.
The transmission sequence is initialized with the command (command code: 1615) when binary code (format 5) is used.
When performing the following at an external device, send the EOT/CL to the C24 depending on the format used.
• Canceling a read/write request by command previously sent. (If a write request is issued, the write request cannot be
canceled when the data has already written to the CPU module.)
• Placing C24 into the wait state to receive commands before commands are sent.
• Placing C24 into the state where it has been started up when data communication cannot be performed normally.
The message structure when sending EOT, CL is shown below.
Only the following data is sent. The station No. and PC No. are not required.
When C24 receives EOT or CL, it proceeds as follows.
• C24 terminates any read/write processing performed to the CPU module upon request from the external device. In this
case, C24 does not send a response message to the command previously received.
• C24 initializes the transmission sequence of the MC protocol from which the EOT/CL is received on the interface side and
placing C24 into wait state to receive commands from an external device.
• C24 does not send a response message to the EOT or CL reception. (It does not send anything to external devices.)
• When it receives EOT or CL while the on-demand function (data transmission function from the CPU module to external
devices) is being performed, C24 terminates to transmit the on-demand data to external devices. (Page 280 On-
demand function)
Symbol name Description Code (hexadecimal)
STX Start of Text 02H
ETX End of Text 03H
EOT End of Transmission 04H
ENQ Enquiry 05H
ACK Acknowledge 06H
LF Line Feed 0AH
CL Clear 0CH
CR Carriage Return 0DH
NAK Negative Acknowledge 15H
Format EOT CL
Format 1 to format 3
Format 4
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