WIZ550S2E not responding to "+++"

Following on from my 12th May post about the loss of data on a corporate network.

We are still trying to get this application working. What we have seen is that the WIZ550S2E module does not respond to the “+++” trigger to get into command mode if there is no Internet connection on the LAN network. the module has 1.4.0 firmware

It also does not respond to +++ if the Ethernet cable is not plugged into the module. this is less of an issue.

We have a data mode set up but are now primarily using Command Mode to send/receive data.

Any suggestions?



Hello @jcomfort,

Entering into command mode is possible even if the ethernet cable is not connected.

When entering ‘+++’, did you enter CR/LF(\r\n) after ‘+++’?

When entering ‘+++’, you do not need to enter CR/LF(\r\n) at the end.

I tested with ethernet cable removed in F/W v1.4.0. But there was no problem.

Please refer to the picture below as the test result.

Hi Austin,

Thanks for your comments.

I have just done some more testing this on this with some brand new WIZ550S2E units (which actually have version 1.4.1 firmware).

First time they are used, you are correct, they do respond to “+++” with the LAN cable disconnected.

Our application goes through the following sequence of commands once we have a response to the “+++” command:




AT+NSET=D, only sent if the unit is not in DHCP mode from the previous command

AT+NSTAT after a short delay, to read the allocated IP address




We then respond to [R…] messages and send using AT+NSEND commands in our application.

After a brand new unit has been through this sequence, it no longer responds to the “+++” on power up when the LAN cable is not plugged in.

For info, the new units are F/W version 1.4.1 and we do not send a CR LF after the “+++” – our sequences are fully recognised with the cable plugged in. (We also wait for the [S…] responses before doing the next command in the initialisation sequence.

If I do a Factory Reset on the module (hardware or using the configuration tool) the module does respond again to the “+++” on power up with the LAN cable unplugged.

Any thought or suggestions?

Thanks and best regards


John Comfort

JCA Systems Ltd

Hi Austin,

After some more testing I think I have isolated where the problem might be.

If the unit is set with DHCP ON at power up, it doesn’t respond to “+++” unless the Ethernet cable is plugged in.

Best regards


Hi @jcomfort,

Even in a state set to DHCP, it is also possible to enter the command mode with ‘+++’.

However, if it is set to DHCP, unlike STATIC, it goes through a DHCP loop, so it cannot enter the command mode with ‘+++’ until it exits the DHCP loop.

That is, it takes quite a long time to enter the command mode in the state of being set to DHCP.

Because WIZ550S2E is the S2E(Serial to Ethernet) module, it is recommended to use ethernet cable in connected state by default unless there are specific reasons to use it in unconnected state.