Unlike modular PLCs such as the Q-Series, FX PLCs have default settings for retentive/latched device words, but memory, timers, etc. While this is not an issue, it does need to be taken into consideration when creating PLC programs.

Design Considerations

All FX PLCs have retentive or latched word and bit devices as stated above. In a FX3U PLC for example, there are 2 types retentive or latch but (M) devices as can be seen from the extract below from the FX PLC programming manual, chapter 4.3.1.

The latch (battery backed) type M500 to M1023 can be set or changed within the PLC programming software, in the device settings of the PLC parameters as shown below.

GX IEC Developer system variables

GX IEC Developer download options that reset system variables to zero

Further Information

For further information, see the FX PLC programming manual together with download settings within GX IEC Developer.