Chapter 3 Analog Output Timing/ControlDAQ-STC Technical Reference Manual3-114 ©National Instruments Corporation3.8.2 Trigger Selection and ConditioningThe signal routing block selects the counter clocks, trigger signals, and gate signals from thedefault timebases. The routing logic for the UI_SRC, UI2_SRC, and BC_SRC signals is a20-to-1 multiplexer followed by an exclusive OR gate for polarity selection. The routing logicfor the trigger signal START1 has additional controls for edge detection and synchronization,as shown in Figure 3-35. When synchronization is selected, START1 is synchronized to bothUI_SRC and BC_SRC.UI2_CE UI2 Count Enable—This signal enables and disables the UI2 counter.Refer to section 3.8.3.8, UI2 Control, for the UI2_CE equations.UI2_CLK UI2 Clock—The UI2 clock signal is the actual clock for the UI2counter and the UI2 control logic. When the counter is not armed,UI2_CLK is the write strobe for AO_Command_1_Register, so thatthe counter can be loaded using the load command. When the counteris armed, UI2_CLK is the same as UI2_SRC.UI2_LOAD UI2 Load—This signal pulses to load the value from the selected UI2load register into the UI2 counter. Related bitfields: AO_UI2_Load.UI2_LOAD_SRC UI2 Load Source—This signal determines which load register, A orB, the UI2 counter will use on the next reload. The initial UI2 loadsource is set using AO_UI2_Initial_Load_Source. The UI2 controllogic updates UI2_LOAD_SRC while the DAQ-STC is counting.The current load source depends on the counter state and the selectedreload mode. Related bitfields: AO_UI2_Initial_Load_Source,AO_UI2_Next_Load_Source_St, AO_UI2_Reload_Mode.UI2_SRC UI2 Source—The UI2 source is the timebase for the UI2 counter. Itis software selectable from AO_IN_TIMEBASE1, IN_TIMEBASE2,the G_TC signal from general-purpose counter 0 or 1, PFI<0..9>, andRTSI_TRIGGER<0..6>. Related bitfields: AO_UI2_Source_Select.UI2_TC Secondary Update Interval TC—The UI2_TC signal is theindependent secondary update interval clock.Table 3-6. Internal Signals (Continued)Signal Description
