I have a sensor probe with 4 Photodiodes and want to use 2 PD Channels. Channel 1 is routed to TIA1, channel 2 to TIA2. When I measure both channels witch Single Receive Mode everything works fine. When changing to Dual Mode (TIA_SEL = 3) I don't receive a useful signal. Are there an additional steps necessary to activate the Dual Receive mode?