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4 THE EXCHANGE BETWEEN THE PLC AND BUFFER MEMORY
4.3 Communication with the Buffer Memory
PLC CPU Device
23
H
D1
(H)
00
H
D2
(H)
00
H
D3
(H)
4 - 20
There are 6 Kbytes of buffer memory in the communications module that can be read
and written by the FROM and TO instructions from the PLC. Vast amounts of data can
be communicated with the PLC CPU using this area. The PUTMEM and GETMEM
instructions are used to access the buffer memory from BASIC.
The buffer memory addresses differ from when designation is performed from the PLC
CPU and from the AD51H-BASIC. The differences are shown below.
(Address)
PLC CPU side
The addresses from the PLC CPU side are in lead units, but the BASIC side
addresses are in byte unites. Therefore, BASIC uses 2 addresses when 1-word data
are being handled and 4 addresses when 2-word data are being handled. Note the
following when specifying addresses in BASIC.
Actual data flow shows as follows.
• For numeric value data
45
H
(L)
12
H
(L)
FROM
18
/TO
H
(L)
Accessed using
(
Address 7
H
through 9
H
PLC CPU Side
REMARK
For details on FROM/TO instructions, refer to the ACPU Programming Manual
(Common Commands Edition).
Buffer Memory
(Address)
0
0
H
1
2
1
H
3
4
2
H
5
6
3
H
7
17FE
BFF
H
17FF
Buffer Memory
45
(L)
E
H
H
7
H
F
23
(H)
H
H
12
(L)
10
H
H
8
H
11
00
(H)
H
H
18
(L)
12
H
H
9
H
00
(H)
13
H
H
)
(
AD51H-BAISC side
H
H
H
H
H
H
H
H
H
H
Integer Variables,
Integer Arrays
RD% (0)
RD% (1)
GETMEM
RD% (2)
/PUTMEM
Accessed using
)
Address E
H
through 13
H
AD51-BASIC Side
MELSEC-Q
23
(H)
45
(L)
H
H
00
(H)
12
(L)
H
H
00
(H)
18
(L)
H
H
4 - 20
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