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8. COMMUNICATIONS USING DEDICATED PROTOCOLS
MELSEC-A
8.2
Programming Hints
8.2.1
To write data to the special use area i n buffer memory
(1)
Buffer memory is not 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. Data changed from the default
values must be written t o the buffer memory whenever the power is
turned ON or the CPU is reset.
(2) Only TO instruction can be used t o write data to the special use area
(100H to 11FH).
If data is written t o the buffer memory using the
command in a computer program, the AJ71 C24 will not operate correct-
ly. Never try t o write data using a computer program.
(3) If the following functions are used i n combination with the dedicated
protocol, make sure to 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 to different functions, the data in this area
is rewritten and communications will not be correctly executed.
*NO-protocol mode transmission or bidirectional mode transmis-
sion
NO-protocol mode receive or bidirectional mode receive
Buffer memory readlwrite (CRICW command) function
On-demand function
The memory areas preceding and following the special use area cannot
be allocated as a single area. The areas OH to FFH and 120H to 7FFH
must be recognized as independent areas.
Example:
The on-demand buffer area cannot
be allocated in this manner
(4)
If the designation is made to process the sendlreceive data in the
no-protocol mode or bidirectional mode in units of words or bytes, the
on-demand data is processed in the same designated unit.
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