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10. COMMUNICATIONS IN THE BIDIRECTIONAL MODE
MELSEC-A
10.5.2
Message
format
(1) Control code
Signal
C o d e
I
N a m e
I
(hexadeclrnal)
1
Meaning
/
Application
I
ENQ
I
05H
I
Enquiry
I
T h e code used to begin data send.
ACK
(a) Data send from an AJ71C24 to a computer
NAK
The AJ71 C24 appends the control code to be transmitted,
06H
(b) Data send from a computer to an AJ71C24
15H
The AJ71C24 checks the control code received. It is not possible
to read the control code from a sequence program.
Acknowledge
(2)
Data length
The code returned to the mating station
when data has been received correctly.
Nagative
Acknowledge
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.
The code returned to the sending stations
when data has not been receiving correctly.
(immediately followed by an error code)
(a) Data send from an AJ71C24 to a computer
The data length to be transmitted is the value written to the send
data length storage area of the AJ71C24 buffer memory by the TO
instruction in a sequence program.
The AJ71C24 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 "AJ71C24:" and value "100"
(units: bytes)
I-------------
Data a r e a - 4
Computer
E
Q
05.
AJ71 C24
(L)
Data
length
OOOAH
( Y .
,
m .
10 bytes
b15
(2
be
b7
to
bl bO
ill
Bit data
..R
'y
n7',u1s . . C u
,,2.. .,4..
,,:.,;
0 0 6 4 ~
'
( l o o )
4,.
,
a .
,a.
,,I"
,
I , " ,
,>.
,
% ,
x.;
a<.,
m.
expressing
Check
sum
0 2 4 4 ~
4'.
,
0 2 .
"1
0
P
(HI
O O H
OAH
0 0 0 0 0 0
0
0 0 0 0 0
1
1
0
0
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