10.
COMMUNICATIONS IN THE BIDIRECTIONAL MODE
MELSEC-A
(b) Data send from a computer to an
AJ71C24
The
AJ71 C24
checks and processes the check sum received.
It
is
not possible to read the check sum from a sequence program.
When the setting is "check sum is disabled", the received data
following the data of the designated length is ignored
up
to the next
control code.
Example: Check sum when transmitting
"AJ71C24:"
and value
"100'
(units: bytes) is processed as follows.
1
OAH
+
OOH
+
41H
+
4AH
+
37H
+
31H
+
43H
+32H+34H+UH+64H+OOH
9
Sum
=
G244H
b15
k
b8
b7
bl
bo
~rycont~-0000000000001010
st
0144H
am
44H
0
L
I
I
M
e-
''
?r
L
II
(5)
Error code
An
error code indicates the error content when an
NAK
response is
received. The code is transmitted and received
in
the range of
0001
H
to
OOFFH.
Section
11.2
gives error code details.
(a) Data send from an
AJ71 C24
to
a
computer
The
AJ71 C24
appends the error code.
When transmitting an error code, the
AJ71 C24
writes the same error
code to its error code storage area in the received data buffer
memory area.
(b) Data send from a computer to an
AJ71 C24
The
AJ71C24
writes the received error code to the error code
storage area in its send data buffer memory area.
POINTI
I
In bidirectional communications, check sum and error codes are all binary
data. Note that in the dedicated protocol, they are handled
in
ASCII
code.
I
I
10- 16
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