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8. COMMNICATIONS USING DEDICATED PROTOCOLS
MELSEC-A
8.9
Buffer Memory Read and Write
This function is used to read from and write t o the AJ71C24 buffer memory.
When this function is used, communications between the computer and
AJ71C24 commences immediately when the computer sends a read or write
request, without waiting for the PC CPU END processing. Therefore, the
time T I , described in Section 8.5, is always equal to zero. The PC CPU
carries out buffer memory read and write using TO and FROM instructions.
The method for specifying the control protocol, meanings, and examples for
carrying out this function are shown below.
8.9.1
Commands and buffer memory
(1) ACPU common commands
Command
Processing
Item
(2)
Buffer memory
Number of
State
of PC CPU
Points
Processed
per
During RUN
tions
Batch
read
Batch
write
Buffer memory addresses are O H to 7FFH see (see Section
3.5)
One address consists of 1 word (1 6 bits).
Read and write are both executed in word units, regardless of the
Note
:
o
..........
Executable
CR
CW
wordlbyte unit setting.
POINTI
(1) When accessing the user area in buffer memory simultaneously by
using this function in the no-protocol mode (see Section 9) or the
bidirectional mode (see Section l o ) , the buffer memory address in the
following area should not be designated by the command described
in item (1) in Section 8.9.1.
43H, 52H
43H. 57H
I
0
No-protocol mode send area (or bidirectional mode send area)
1
0
No-protocol mode receive area (or bidirectional mode receive area
Reads from buffer memory.
Writes to buffer memory.
I
0
On-demand area
(2) Buffer addresses 1 O O H to 11 FH comprise the special applications
area. The AJ71C24 will not operate correctly if any operations other
than those described in the following sections are executed.
64 words
(1
28 bytes)
0
0
0
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