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MELSEC-Q
4 THE EXCHANGE BETWEEN THE PLC AND BUFFER MEMORY
4.3 Communication with the Buffer Memory
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.
0
H
1
H
2
H
3
H
4
H
5
H
6
H
7
H
17FE
H
17FF
H
BFF
H
0
H
1
H
2
H
3
H
Buffer Memory
(Address)
(Address)
PLC
PLC CPU side
BASIC
AD51H-BAISC 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
( )
Accessed using
Address E
H
through 13
H
23
H
(H)
45
H
(L)
00
H
(H)
12
H
(L)
18
H
(L)
00
H
(H)
RD% (0)
RD% (1)
RD% (2)
45
H
(L)
23
H
(H)
00
H
(H)
12
H
(L)
18
H
(L)
00
H
(H)
Buffer Memory
PLC CPU Device
23
H
(H)
00
H
(H)
45
H
(L)
12
H
(L)
18
H
(L)
00
H
(H)
D1
D2
D3
( )
Accessed using
Address 7
H
through 9
H
7
H
8
H
9
H
E
H
F
H
10
H
11
H
12
H
13
H
Integer Variables,
Integer Arrays
FROM
/TO
GETMEM
/PUTMEM
AD51-BASIC Side
PLC CPU Side
REMARK
For details on FROM/TO instructions, refer to the ACPU Programming Manual
(Common Commands Edition).
