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10. COMMUNICATIONS IN THE BIDIRECTIONAL MODE
MELSEC-A
10.5.2
Message format
(1)
Control code
(a) Data send from an AlSJ71C24 to a computer
Signal
Name
ENQ
ACK
NAK
The AlSJ71C24 appends the control code to be transmitted.
(b) Data send from a computer to an AlSJ71C24
a
The AlSJ71C24 checks the control code received. It is not possible
to read the control code from a sequence program.
Code
(hexadecimal)
05H
06H
15H
(2)
Data length
Meaning
Enquiry
Acknowledge
Nagative
Acknowledge
Application
The code used to begin data send.
The code returned to the mating station
when data has been received correctly.
The code returned to the sending stations
when data has not been receiving correctly.
(immediately followed by an error code)
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 A1 SJ71 C24 to a computer
The data length to be transmitted is the value written to the send
data length storage area of the A1 SJ71 C24 buffer memory by the TO
instruction in a sequence program.
The AlSJ71C24 transmits the written value as it is from the lower byte
(L).
(b) Data send from a computer to an AlSJ71C24
The AlSJ71 C24 checks the received data length. When
it
is correct,
a
the AlSJ71C24 writes the first 1 byte to the lower byte position (L)
of the received data length storage area of the AlSJ71C24 buffer
memory.
a
Example: Data length when transmitting "AlSJ71C24:" and value "100"
(units: bytes)
a
Data
computer
E
N
Q
~n
A1 SJ71 C24
(L)
Check
sum
02CAn
c w , m
Data
length
O O O C ~
.
12 bytes
b15
v
bs b7
I : !
bl
M
" A .
.J.
-F
"I
. .
-c
.4..
v:.
;
0064n
(loo)
~ ~ , J I * , u * , u I , ~ , ~ ~ , u I , ~ , s u , ~ Y ~ I ,
m
Bit data
expressing
' 1
2 '
(H)
O O H
OCH
0
I
0
1
0
0
0
0
0 0 0 0 0 0 0 0
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