Mitsubishi MELSEC LJ71C24, User Manual

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11 DATA COMMUNICATION USING THE BIDIRECTIONAL PROTOCOL
11.3.2 Communication data processing when simultaneous transmissions occur
Examples of the C24 communication data processing for the "Transmission data" and
"Receive data" settings by GX Works2 are explained.
(1) Transmission: Valid, Receive: Valid
C24 side
External device
Arbitrary data
E
N
Q
Sum check
code
Arbitrary data
E
N
Q
Sum check
code
A
C
K
A
C
K
Time check
(timer 1)
1)-2 2)-1
1)-1 2)-2
POINT
When the entire message of 2)-1 was received while transmitting the message of
1)-1 in the illustration:
• The C24 turns ON Receive read request (X3/X4) of 2)-1 after sending all of 1)-1.
(2) Transmission: Invalid, Receive: Valid
External device
Arbitrary data
E
N
Q
Sum check
code
Arbitrary data
E
N
Q
Sum check
code
A
C
K
2)-1
1)-1 2)-2
Ignores the receive
data of 1)-1.
(Generates a simultaneous
transmission error.)
C24 side
(3) Transmission: Valid, Receive: Invalid
External device
E
N
Q
E
N
Q
A
C
K
1)-2 1)-1
1)-1
C24 side
Time check
(timer 1)
Ignores the receive
data of 2)-1.
Arbitrary data
Sum check
code
Arbitrary data
Sum check
code