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10. COMMUNICATIONS IN
THE BIDIRECTIONAL MODE
MELSEC-A
10.3.2
To write data t o a special applications area in buffer memory
(1)
Buffer memory is not battery backed up by a battery
All data in buffer memory is set to the default values when power is
turned ON or when the PC CPU is reset.
The data changed from the default values must be written whenever the
power is turned ON or the PC CPU is reset.
(2)
Only TO instruction can be used to write data t o the special applications
area (1 00H to I
I
FH).
(3) If data is written using the command in a computer program, the
AJ71C24 will not t o operate correctly. Never try t o write data using a
computer program.
If the following functions are used in combination with the dedicated
protocol, allocate the user area in buffer memory so that the same area
will not be used by different functions.
If the same area is allocated t o different functions, the data in this area
is rewritten and communications will not be correctly executed.
b
Bidirectional mode send
b
Bidirectional mode receive
b
Buffer memory readlwrite (CR/CW command) function
b
On-demand function
The memory areas preceding and following the special applications
area cannot be allocated as a single area. The areas of O H to FFH and
120H t o 7FFH must be recognized as independent areas.
Example:
I
FFH
l o o n
The buffer
area cannot
be allocated
in this
number
(4)
If designation is made t o process the sendlreceive data in the bidirec-
tional mode in units of words or bytes, the on-demand data with the
dedicated protocol is processed in the same designated unit.
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