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8.
COMMUNICATIONS USING DEDICATED PROTOCOLS
MELSEC-A
(b) Half-duplex communications
l ~ o m p u t e r is transmitting data1
On-demand function executing
( 1 )
/
1
TO instruction to buffer memory
PC CPU
addresses 109H and lOAH
1) The on-demand function executing signal (Xn3) turns on imme-
diately when the on-demand request is made.
2)
Transmission of on-demand data is suspended until the comple-
tion of command data receive (beginning with ENQ) from the
computer.
3) Transmission of response data (beginning with STX) to the
command data (beginning with ENQ) is suspended until the
completion of on-demand data transmission.
[computer is receiving data(
On-demand data
On-demand function executing
Xn3
TO instruction to buffer memory
)
PC CPU/
addresses 109H and lOAH
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
completion of the response data (beginning with STX) t o the
command 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 AJ71C24 should be made after the completion of
on-demand data receive.
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