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10. COMMUNICATIONS
IN THE BIDIRECTIONAL MODE
MELSEC-A
10.5 Bidirectional Communications Basics
10.5.1 Control protocols
Contents
ransmission
om a PC
:PU to a
omputer
,n AJ71 C24
sceives
ata from
computer
lemark
Protocol
Direction of
transmission
a
Computer
(nor-
send)
,
AJ71C24
Time-out check time
is set at address
113H of the buffer
memory
Addition within
(1) Check sum exists only when
" 0 '
is set to address 115H of buffer memory.
(2) Check sum is calculated within the area indicated by
*I.
(3)
The AJ71C24 returns an NAK immediately if it detects an error
as
in '2 while communications is
made in the fuli-duplex mode. In half-duplex mode communication, it returns an NAK only after the
data has been received.
The AJ71C24 ignores receive data if it detects an error (Section 10.3.3 (5)). Therefore, it does not
give a received data read request to the PC CPU.
Direction of
transmission
Addition within this range
a
i
Computer
E
AJ71 C24
*2
Data
length
Received data read request
Vnl)
Received data read completed
Ccl"
+
111)
'
Error
code
L , H
Data area (Received
data to be transferred to
sequence program)
(abnormal receive)
Check
L , H
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