4 - 19 4 - 19
MELSEC-Q
4 THE EXCHANGE BETWEEN THE PLC AND BUFFER MEMORY
(3) When using an internal device as a data storage area (when using
ED and EM)
(a) Bit device
Bit devices are handled in bit units or word units. The following describes
each of them.
• Bit units
When bit unit designation is used, the internal bit device EM is used and
the specified device and EM are matched one-to-one correspondence.
Only the designated points are stored and set.
The status of each bit is “0” when the corresponding device is OFF and
“1” when it is ON.
20 bits of data are accessed
from X10 using EM0 through
EM19.
to
X10
to
1
1 1 0
1
1 1 0
0
0 0 0
1
1 1 1
0
0 1 1
X23 to X20 X1F
X18 X17
to
EM0
to
1
1 1 0
1
1 1 0
0
0 0 0
1
1 1 1
0
0 1 1
EM15
EM8 EM7
EM19 to EM16
• Word Units
When bit devices are designated using word units, the 16 points of
ON/OFF data for each ED will be paired with each bit using word device
ED, then stored and set from the lowest bit of ED.
The status of the each bit is “0” when the corresponding device is OFF
and “1” when it is ON.
M75
to
Corresponds
to M60
to
ED0
One word (16 bits) of data from
M60 is accessed using ED0
to
M60
to
M75
M68 M67
to
b0
to
b15
b8 b7
M68 M67
REMARK
Access • • • I/O processing such as data read and write.
(b) Word devices
When word devices are designated in word units, the internal word device
ED is used to store and set one point of word device data for one ED.
ED0
ED1
ED2
1 2 3
4 5 6
7 8 9
D10
D11
D12
1 2 3
4 5 6
7 8 9
3 words of data from
D10 are accessed
using ED0 through ED2.
