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10. COMMUNICATIONS IN THE BIDIRECTIONAL MODE
MELSEC-A
(b) Data send from a computer to an AJ71C24
The AJ71C24 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.
Ixample: Check sum when transmitting "AJ71C24:" and value "100"
(units: bytes) is processed as follows.
I . -
Data area
- 4
(5)
Error code
Computer
*
Sum
=
(3244H
b15
2
bB
b7
b I M
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.
Aemorycontents-
(a) Data send from an AJ71 C24 to a computer
AJ71 C24
1
O A H + O O H + 4 1 H + 4 A H + 3 7 H + 3 1 H + 4 3 H
+
32H
+
3 4 H
+
3AH
+
6 4 H
+
OOH
E
Q
0%
The AJ71C24 appends the error code
~t 01 44H
t
44H
(L)
0
When transmitting an error code, the AJ71C24 writes the same error
code to its error code storage area in the received data buffer
memory area.
~ a ' t s
length
OOOA
LV-
,
M-
(b) Data send from a computer to an AJ71C24
0
The AJ71C24 writes the received error code t o the error code
storage area in its send data buffer memory area.
,w
I "
m7"m1,,
,,C"
I "
, c 4"
,,:"I
0 0 6 4 ~
:
(100)
I l * ,
4""
,
37"
,
38.
,
4 3 " )
J & ,
341,
3.'
6,"
M.
In bidirectional communications, check sum and error codes are all binary
data. Note that in the dedicated protocol, they are handled in ASCII code.
Check
I
SL
02.
0 .
0 0 0 0 0 0 0
0
0 0 1 0 1 0
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