User`s manual

208
(2) DC2/DC4 transmission control, DC2/DC4 reception control
The Q series C24 encloses the send data from the local station in the DC2 and DC4 codes and transmits it to the
external device and processes the data received from an external device enclosed in the DC2 and DC4 codes as
valid data.
DC2: Control data that informs the external device that the data following it is the start of the valid data
DC4: Control data that informs the external device that the data immediately preceding it is the end of the valid
data
(a) Q series C24 DC2/DC4 transmission control contents
When transmitting data to an external device, the Q series C24 adds the DC2 code to the head of the send
data and the DC4 code to the end of the send data.
(b) Q series C24 DC2/DC4 reception control contents
• When the Q series C24 receives DC2 from the external device, it processes the receive data up to DC4 as
valid data. The sequence program cannot read the received DC2 code.
• When the Q series C24 receives DC4, it ignores the receive data up to immediately before DC2 as invalid
data. The sequence program cannot read the received DC4 code.
• Once DC2 is received, subsequent DC2 are ignored and are removed from the receive data.
DC2 DC4
DC2 DC4
DC2External device
Programmable
controller CPU
Data Data
Data
D
C
2
D
C
2
D
C
4
D
C
4
E
N
Q
*
External device
Programmable
controller CPU
Data
Data length
Sum check
Data
Transmit order
(Non procedure protocol)
Transmit order
(Bidirectional protocol)
The DC2 and DC4 code are also added when MC protocol is used.
D
C
2
D
C
2
D
C
4
D
C
4
External device
Programmable
controller CPU
Data Data
Arbitrary
data
Stored to Q series C24
buffer memory or OS area
Ignored by
the Q series C24
(Non procedure protocol)
*1
Stored to Q series C24
buffer memory or OS area
D
C
2
E
N
Q
D
C
4
*1
Character
External
device
Station No. PC No. Command Message wait
Sum check code
MC protocol A
compatible 1C frame
format 1