1st time turning on 2406B after 6.40 -> 6.51 firmware upg


in our devices the ON/OFF pin is set to HIGH for 3 seconds when the device is turned on by pressing the power button.

When we upgrade the firmware from 6.40 to 6.50a or 6.51 this does not seem to be enough. Actually, we are no longer able to turn on the device anymore by the power button. (if we managed the first time by bypassing the power button, the device will go back to regular operation…)

Is this because there is some kind of initialization when the module is turned on for the first time after the firmware download? What time is required to be safely able to turn on after any update? Even if there is some initialization process required, why does the module shut down if the ON/OFF pin is released after 3 seconds?

Thanks in advance,



This is certainly due to some initializations in internal flash memory which take few seconds after an upgrade.

Perhaps you are switching-off the module too early after the end of the download.

If you are using XModem (or 1K-XModem) to upgrade, then after the end of the download you have to send AT+CFUN=1 command and wait for the OK answer.
Also, send AT (or ATI3 to check the software version) and wait for the answer to be sure the module is OK.
Then only after that you can switch off the module.

With a such upgrade process you should have no problem to turn on the module.


Of course I did send AT+CFUN=1. This command will turn the module OFF.

And there is no OK. This is a new feature since Open AT 3.0, I think. Before, with Open AT 2.0 there was an OK after turning on the device again after AT+CFUN=1. With the new firmware this OK will not be sent anymore. It has been eliminated, from what I heard on purpose because it did cause problems in certain applications where the module is connected to a microprocessor…

So, there’s no OK anymore.

If you can see an OK appear quickly after sending AT+CFUN=1 your ON/OFF or CHARGE/IN pin is set to be constantly HIGH, and you are using an older firmware version.

I can’t send AT or ATI3 when I am not able to turn on the module. It won’t respond :wink:

Sorry, I forgot to mention: Yes, I am using 1k-XModem. When we are upgrading with the module on our PCB, we do not have access to the Boot-/On-off pins, so we can’t flash using DWLWin.