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8.
COMMUNICATIONS USING DEDICATED PROTOCOLS
MELSEC-A
(b) Half-duplex communications
Computer is transmitting data
On-demand function executing
( 1 )
/
Computer
TO instruction to buffer memory
addresses 109H and 10AH
1) The on-demand function executing signal (Xn3) turns on imme-
diately when the on-demand request is made.
A1 SJ71 C24
S
T
X
E
2)
Transmission of on-demand data is suspended until the comple-
tion of command data receive (beginning with ENQ) from the
computer.
(2) On-demand data
1
(3)
3) Transmission of response data (beginning with STX) to the com-
mand data (beginning with ENQ) is suspended until the comple-
tion of on-demand data transmission.
IComputer is receiving data1
On-demand function executing
/
Xn3
(2)
TO instruction to buffer memory
addresses 109H and 10AH
1) The on-demand function executing signal (Xn3) turns ON imme-
diately when the on-demand request is made.
2)
Transmission of the on-demand data is suspended unil the com-
pletion of the response data (beginning with STX) to the com-
mand data (beginning with ENQ).
3) Transmission of the response data (beginning with ACK) from the
computer in response to the response data (beginning with STX)
from the AlSJ71C24 should be made after the completion of
on-demand data receive.
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