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Why is my 5V device not working with my new M238 PLC?

Title

Why is my 5V device not working with my new M238 PLC?

Issue

An external device that is powered by the 5V supplied by the serial port does not work with a new M238 
 
Product Line

Modicon M238 

Environment
 
Cause

Depending on the M238, the voltage supplied by the serial port across pin 7 may not be 5V. The M238's that are PV19 and lower should have the appropriate 5V. The M238 that was released as PV20 had some changes made to some internal components the changed the voltage output of the serial port to less than 5V.

Resolution

To resolve the issue of a 5V device not powering up through the serial port, is to first determine if the M238 is PV20. If the M238 is PV20 then an external 5V power supply will be needed. There are two options that can be used to supply the 5V. The easiest way is to purchase the XBTZRTPW adapter cable or it would be possible to remove the wires from pins 7 (+5V)  and 8 (0V) on the RJ45 connector on the PLC side then connect into a 5V power supply. Schneider does supply a 5V power supply which is the AML8MEM05040.

See attachment for an example diagram.

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