As a general principle, it is always possible to upgrade an application running in an old FX PLC to a newer FX PLC. However there are sometimes slight differences that must be taken into account.

This document will point out the things that need to be considered in a FX PLC upgrade when using pulsed outputs and their associated special M coils and instructions.

Design Constraints

The example used in this document will be an upgrade from a FX1S PLC to an FX3U PLC. The application will use the first 4 high speed outputs Y0 to Y4, the DRVA instruction and several special M coils in the M8000 range.

GX Developer and/or GX IEC Developer software will “convert” a FX1S application to a FX3U but this does not mean that this is the only action necessary to complete the conversion. From the point of view of the DRVA instruction and other associated pulse output instructions no changes are required.

If the special M coils in the M8000 are used, then changes to the program will be required as follows:

Special M Coils used by the FX1S in its program:

Equivalent Special M Coils that have to be used in the FX3U program:

Points to note:

  • Special M coils are not converted when the PLC program is changed to a FX3U.
  • The power consumption of the FX3U PLC can often be higher than the equivalent FX1S (example: for a 24dc powered 30 I/O PLC, the power consumption of FX1S is 8 watts but the FX3U is 30 watts).

Further Information

For further information, see the PLC programming manual.

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