Mitsubishi Electric MELSEC-A Series Manual page 141

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REPLACEMENT OF MELSECNET (II) AND /B (REMOTE I/O NETWORK)
(3) Sequence program
(a) Data separation prevention
When two words (32 bits) or more of cyclic data (e.g. current value of the positioning module) are
handled, the old data sometimes is mixed with the new data. To read/write cyclic data of two words or
more in a single operation, set data separation prevention by the per-station block guarantee
function.
By enabling the per-station block guarantee function, handshaking is performed between CPU
modules and network modules to refresh the network and to enable data separation to be prevented
in station units. The per-station block guarantee function is enabled when "Secured data send" and
"Secured data receive" in the following parameters are set. Enabling the per-station block guarantee
function is recommended.
(b) I/O assignments
The I/O assignment function is used to reserve and set module information to prevent I/O numbers
from deviating even if a module is mounted later on in an empty slot, and to conserve the number of
I/O points.
With MELSECNET/H, each of the I/O assignments are set on each remote I/O station. With
MELSECNET (II), however, as the I/O assignments of all remote I/O stations were set on the master
station CPU. Set the I/O assignments of each remote I/O station again at transition to
MELSECNET/H.
Also, as the I/O assignment settings of PLC parameters are not cleared when the programmable
controller type is changed (e.g. when A3ACPU is changed to Q06UDVCPU), manually clear the I/O
assignment settings for the remote I/O stations.
(c) Processing time
The link scan time and link refresh time differ between the A/AnS/QnA/QnAS series and the Q series.
For details on processing times, refer to the manual for the respective module.
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