Mitsubishi Electric MELDAS C6 Programming Manual page 315

Restrictions in Using FROM/TO Command
Using FROM/TO command by the built-in PLC in C6/C64 has the restrictions below.
(1) The number of FROM and TO commands that can be used in one scan (including multiple
program) is 50 each. Using more than 50 will cause the alarm "Q01 EMERGENCY STOP LAD
0005", and will stop the built-in PLC.
(2) The accessible size of buffer memory in one scan (including multiple program) by FROM/TO
command is up to 12k words. Exceeding 12k words will cause the alarm "Q01 EMERGENCY
STOP LAD 0006", and will stop the built-in PLC.
(3) Actual transfer from the buffer memory to read devices by FROM command, and transfer from
write devices to the buffer memory by TO command are done at the execution of END command.
(In multiple programs, at the execution of END command at the end of all the programs.) Thus,
device data renewal will be delayed by 1 scan.
Token p-
articip-
at. sta-
tus sig.
Other n-
ode area
1 data
ref dev.
(4) FROM/TO commands cannot be used in high-speed program processing.
If FROM/TO command is executed in high-speed program processing, the alarm "Q01
EMERGENCY STOP LAD 0007" will occur and the built-in PLC will stop.
(5) If bit device is used for FROM/TO command, the only available unit for designation is 16 bits.
If bit device is not designated in the unit of 16 bits, the alarm "Q01 EMERGENCY STOP LAD
0008" will occur and the built-in PLC will stop.
Correct example : FROM H0 H1C00 K4B20 K32
Incorrect example : FROM H0 H1C00 K4B28 K32
9. Exclusive Commands 1
FROM, TO
TO H0 H1C80 K4M64 K32
TO H0 H1C80 K4M100 K32
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Head of
node 01
area 1
readdata
Head of
node 03
area 1
wrt data
Other n-
At this point, a transfer
ode area
1 data
command to B0 to B5F is
ref dev.
issued by the FROM
command, however, the
transfer will not actually be
executed at this point.
Local n-
ode area
1 output
device
The device B0 used here is in
Local n-
the state of the previous scan.
ode area
1 output
device
Actual writing in the devices
B0 to B5F from the buffer
memory by the FROM
command is executed at this
point.
"Q01 EMERGENCY STOP LAD 0008"
"Q01 EMERGENCY STOP LAD 0008"