Programming; Precautions For Creating Programs - Mitsubishi MELSEC-A Series Reference Manual

9.

PROGRAMMING

9 PROGRAMMING
This chapter describes methods for programming the master and local stations to perform
data link among CPU modules.
9.1

Precautions for Creating Programs

(1) Used link devices
The device numbers assigned to each station with link parameter can be used for link
devices (B, W, X, Y) to be used in data link programs.
(2) Writing fail safe programs
Using special link relays (M9200 to M9255) and special link registers (D9200 to
D9255), an interlock should be provided for data link programs among
communication stations so that the other stations data can be used only when the
data link is performed normally.
(3) Data link method for data of two or more words
When writing data of two or more words to the link registers, employ the following
procedure to prevent sending/receiving the data in which the old and new data are
mixed.
(a) When using a module that executes link refresh immediately after link scan
(such as the AnNCPUP21/R21 and the A0J2CPUP23/R23), executing
handshake processing with link relays are recommended so that the link register
data can be read by other stations after the data is written to the link registers.
POINT
Link refresh is performed at the master station and local stations even while an
instruction is processed.
In a program example above, if link refresh is performed when the D0 data is
being transmitted to W0, the new data and old data is stored to W0 and W1
respectively, and sent to the receive station.
MELSECNET mode MELSECNET
MELSECNET
MELSECNET
Operating Mode
mode
mode
Applicability
9 - 1
MELSECNET/B
MELSECNET
MELSECNET MELSECNET MELSECNET
composite mode mode mode composite mode