3.
SPECIFICATIONS
,
,,/_.
MELSEC-A
3.5.5
DCW
send
control
This section describes DC2/DC4 send control.
(1) What is DC2DC4 send control?
When data is sent from the A171 C24 to an external device, the AJ71 C24
adds DC2 and DC4 codes at the beginning and end of data respectively.
3.5.6
DCWDC4
receive
control
This section describes DC2/DC4 receive control.
(1) What is DC2/DC4 receive control?
By using DC2 and DC4 codes, this function determines the data range
'
when the AJ71C24 receives data from an external device.
(2)
Control operations
(a) When the AJ71C24 receives DC2 code from an external device, the
AJ71 C24 handles data in the range between DC2 and DC4 as valid
data.
The received DC2 code
is
not available to the user.
(b) When DC4 code is received from the external device, the AJ71C24
will ignore subsequent received data until another DC2 code is
received.
The received DC4 code is not available to the user.
D
c
Imlwantdata
C
D8h
C
D
D
D
Data
C
4
Extcrmal&vice
2
4
2
f
~ ~~~~
mc24
-
I
u
SbondinMAnlc24
Ignored
by
the
Stored
in
the
buffer
or
OS
receive
area
An1
c24
AJ7lQ4
buffer
or
OS
receive
area
(c) After DC2 code is received,
if
another DC2 code is received, that
code will be ignored, and
will
be removed from the received data.
3-32
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