der mode is required. </p><p class="paragraph"> However, for DFU implementations from older SDKs, where there was no DFU Version characteristic, the service must guess. If this option is set to false (default) it will count number of device's services. If the count is equal to 3 (Generic Access, Generic Attribute, DFU Service) it will assume that it's in DFU mode. If greater than 3 - in app mode. This guessing may not be always correct. One situation may be when the nRF chip is used to flash update on exter