https://devzone.nordicsemi.com/f/nordic-q-a/10142/have-a-firmware-version-able-to-be-sent-over-the-airHi all, I&#39;ve developed a firmware solution for one of my clients. I&#39;ve compiled using Keil, testing it on a board which previously had SD110. Then I delivered .hex file to him, waiting for his feedback. He is only able to download the firmware overen-USTelligent Community 13Mon, 09 Nov 2015 10:13:25 GMThttps://devzone.nordicsemi.com/thread/37611?ContentTypeID=1Mon, 09 Nov 2015 10:13:25 GMT137ad170-7792-4731-bb38-c0d22fbe4515:6448f5c1-956c-48cf-ad34-ba633aaf6f24Vidar Berg<p>Hi,</p> <p>What SDK is the bootloader based on? If it&#39;s from SDK v7.x.x. or later you need to make a DFU distribution packet (.zip) of the .hex file as explained <a href="http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk51.v9.0.0/bledfu_example_image.html?cp=4_1_0_4_3_1_2">here</a>. This is due to additional <a href="http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk51.v9.0.0/bledfu_example_init.html?cp=4_1_0_4_3_1_3">safety check</a> on the image. However, with SDKs prior to version 7 you must send the .hex only, using nRFtoolbox/Master Control Panel on Android or iOS. PC version of MCP is not backwards compatible.</p> <p>For DFU updates you can only combine bootloader and Softdevice. Application update needs to be separate. So if DFU.hex is you bootloader, it needs to be updated separately. Also, the UICR section needs to be stripped from the .hex if you&#39;re converting it to .bin.</p><div style="clear:both;"></div>