11 DATA COMMUNICATIONS USING DC CODE TRANSMISSION CONTROL
11.2 Control Contents of DC Code Control
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11
DC2/DC4 transmission control, DC2/DC4 reception control
C24 encloses the data transmitted from the host station in the DC2 and DC4 codes and transmits it to the target device, and
processes the data received from the target device enclosed in the DC2 and DC4 codes as valid data.
• DC2: Control data that informs the target device that the data following it is the start of the valid data
• DC4: Control data that informs the target device that the data immediately preceding it is the end of the valid data
C24 DC2/DC4 transmission control contents
When transmitting data to a target device, C24 adds the DC2 code to the head of the data to be transmitted and the DC4 code
to the end of the data to be transmitted.
C24 DC2/DC4 reception control contents
• When DC2 is received from the target device, C24 processes the received data up to DC4 as valid data.
The received DC2 cannot be read by the program.
• When DC4 is received from the target device, C24 ignores the received data up to the one immediately before DC2 as
invalid data.
The received DC4 cannot read by the program.
*1 MC protocol 1C frame
• Once DC2 is received, subsequent DC2 is ignored and removed from the received data.
DC2 DC4
DC2 DC4
DC2
Target device Data
Data
CPU module
Data
D
C
2
D
C
2
D
C
4
D
C
4
E
N
Q
Target device
CPU module
Sum check
code
Data length
Data Data
Transmit order Transmit order
(Nonprocedural protocol) (Bidirectional protocol)
The DC2 and DC4 code are also added for communication using MC protocol.
*
D
C
2
D
C
2
D
C
4
D
C
4
(Nonprocedural protocol)
*1
Arbitrary dataData Data
Target device
CPU module
Stored to C24 buffer memory
or OS area
Ignored by the C24 Stored to C24 buffer memory
or OS area
D
C
2
E
N
Q
D
C
4
Station No.
PC
No.
Command
Message wait
Sum check
code
Target
device
Character
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