https://devzone.nordicsemi.com/f/nordic-q-a/35093/packet-receipt-notification-for-serial-dfuHi Support Team, By testing SDK15.0.0/Serial DFU, I find that if we use non-default baud rate(115200), such as 9600 or 38400, we have to assign a non-zero value to -prn(packet receipt notification) option, like below: Otherwise, the nrfutil willen-USTelligent Community 13Tue, 05 Jun 2018 11:21:28 GMThttps://devzone.nordicsemi.com/thread/134712?ContentTypeID=1Tue, 05 Jun 2018 11:21:28 GMT137ad170-7792-4731-bb38-c0d22fbe4515:6e8024b0-9388-44de-887e-7216a0dcb4ddBj&#248;rn Kvaale<p>I believe the PRN sets the number of packets you can send until your receive a packet receipt notification. From my understanding, this means that if you set the PRN to 50, you can send 50 packets before a PRN is generated. Regarding the value to set, I would try a few numbers &amp; see what happens. The picture in the image you sent sets the PRN to 256, so you could try that.</p><div style="clear:both;"></div>