Mitsubishi MELSEC-A Series Reference Manual page 203

7. DATA LINK SETTINGS
(b) The following consistency check is executed when there is difference between
the number of link parameters set for the second tier and the number of link
parameters set for the third tier.
1) When two types of link parameters are set for the second tier and one type of
link parameters is set for the third tier:
The consistency check is executed on the first half link parameters for the
second tier and the first half link parameters for the third tier (including the
MELSECNET mode).
The consistency check is not executed for the second half link parameters for
the second tier.
2) When one type of link parameters is set for the second tier and two types of
link parameters are set for the third tier:
The consistency check is executed on the first half link parameters (including
the MELSECNET mode) for the second tier and the first half link parameters
for the third tier.
The second half link parameters for the third tier are checked whether or not
to begin after the final device number assigned with the first half link
parameters for the second tier.
(c) When the range of link relays (B) and link registers (W) is extended (turning
M9208 and M9209 ON to use), the consistency check will not be executed.
Make sure that the link parameters assigned to the third tier are not also
assigned to the second tier.
Fig 7.34 Assignment when link relay (B) and link register (W) range is extended
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