10.
COMMUNICATIONS
IN
THE
BIDIRECTIONAL
MODE
MELSEC-A
10.5.2
Message
format
(1)
Control code
Moaning
Applkatlon
I
Acknow,dge
The code returned to the mating station
when
data
has been received correctly,
I
I
NAK
1
(a) Data send from an
AJ71C24
to a computer
The
AJ71 C24
appends the control code to be transmitted.
(b) Data send from a computer to an
AJ71 C24
The
AJ71C24
checks the control code received.
It
is not possible
to read the control code from a sequence program.
(2)
Data length
Data length expresses the number
of
bytes or words of data
in
the data
area in 2-byte binary data. Data length units are determined according
to the setting at address
103H
of the buffer memory.
(a) Data send from an
AJ71 C24
to a computer
The data length to be transmitted is the value written to the send
data length storage area of the
AJ71 C24
buffer memory by the TO
instruction
in
a sequence program.
The
AJ71 C24
transmits the written value
as
it
is from the lower byte
(L).
(b) Data send from a computer to an
AJ71 C24
The
AJ71C24
checks the received data length. When
it
is
correct,
the
AJ71C24
writes the first
1
byte to the lower byte position
(L)
of
the received data length storage area
of
the
AJ71C24
buffer
memory.
Example: Data length when transmitting
'AJ71 C24:"
and
value
'100"
(units: bytes)
II
bl5
W
b7
10- 14
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